The  p-erson  charging  this  material  is  re- 
sponsible for  its  return  on  or  before  the 
Latest  Date  stamped  below. 

^ Theft,  mutilation,  and  underlining  of  books 
are  reasons  for  disciplinary  action  and  may 
result  in  dismissal  from  the  University. 


L161— 0-1096 


- f - 

/ 00  ~/o 

//a  - / Ja  J 


' i/*  / 


/2fe  '■/^7 
/^^<}  -/ys" 
^ _ / r / 


/oV 


€Zo  hA 


//4 


^ 7 0 7^  ^ / 


C 


~j(j  'vii-^'f 

mOf  ^ 


M. 


^ A. 


liiJ  1(  4 i 


ICA  /V/3^T. 


I , 


I 


t) 


s 


WORKS  OF  COL.  JAMES  MERCUR 

PUBLISHED  BY 

JOHN  WILEY  & SONS. 


Permanent  Fortifications. 

By  Prof.  D.  H.  Mahan.  Revised  and  brought  up  to 
date  by  Col.  James  Mercur,  U,  S.  Military  Acade- 
my, West  Point  Numerous  plates.  8vo,  half 
morocco,  $7. 50. 

Elements  of  the  Art  of  War. 

Illustrated  with  full-page  and  folding  plates. 
Third  edition.  8vo,  cloth,  $4.00. 

Attack  of  Fortified  Places. 

Including  Siege-works,  Mining,  and  Demolitions. 
Prepared  for  the  use  of  the  Cadets  of  the  U.  S. 
Military  Academy.  lamo,  cloth,  with  folding 
plates,  $2.00. 


tt  3o 


3 a , 


Antwerp, 


Digitized  by  the  Internet  Archive 
in  2016  with  funding  from 

University  of  Illinois  Urbana-Champaign  Alternates 


https://archive.org/details/mahanspermanentfOOmaha 


MAHAN’S 


PERMANENT  FORTIFICATIONS. 


REVISED  AND  ENLARGED 

BY 

JAMES  MEECU^, 

PEOFESSOE  OF  CIVIL  AND  MILITARY  ENGINEERING, 
United  States  Military  academy. 


SECOND  EDITION. 
FIRST  THOUSAND. 


NEW  YORK- 

JOHN  WILEY  & SONS, 

53  East  Tenth  Street. 

1894. 


Copyright,  1887, 

By  John  Wiley  & Sons. 


PREFACK 


In  revising  this  work  for  the  use  of  the  cadets  at  the  Mill, 
tary  Academy,  it  has  been  my  object  to  retain  the  arrange- 
ment and  so  far  as  practicable  the  identical  language  of  the 
original  text.  I am  prompted  to  this  not  only  by  an  affec- 
tionate  respect  for  my  former  instructor,  but  more  espec- 
ially by  a wish  to  give  the  cadets  an  opportunity  to  profit 
by  Professor  Mahan’s  clear,  ‘concise,  and  comprehensive 
statements,  which  are  the  result  of  the  native  ability,  the 
education,  started  in  America,  continued  in  France  under 
Gen.  Noizet,  and  completed  by  a life-long  study ; and  the 
rare  experience  gained  in  over  forty  years’  service  as  Assist- 
ant-professor and  Professor  at  the  Military  Academy. 

The  parts  omitted  and  the  new  matter  introduced  have 
been  selected  with  a view  to  rejecting  only  that  which  has 
become  obsolete  through  the  introduction  of  improved 
'weapons  and  methods,  and  to  explaining  and  illustrating  the 
new  features  developed  from  the  same  causes. 

^ In  making  these  selections  it  has  seemed  better  to  omit 
' ^the  details  of  the  Bastioned  system  as  worked  out  by  Noizetj 
/notwithstanding  its  value  as  a problem  in  fortification-draw- 
ing, and  to  replace  it  by  fuller  treatment  of  detached  works, 
sea- coast  defence,  and  constructions  in  iron  and  steel  as  used 
at  the  present  day. 

My  thanks  are  due  to  Lieut.  G.  J.  Fiebeger,  Corps  of  En- 
' ’ gineers,  for  translations  from  the  German,  and  for  collecting 
O the  information  contained  in  Appendix  II.;  and  to  Lieut. 
^ Geo.  W.  Goethals,  Corps  of  Engineers,  for  compiling 
• ' Appendix  I. 

West  Point,  N.  Y.,  March,  1887. 


CONTENTS 


CHAPTER  I. 

Pkeliminaky  Considerations  and  Component  Elements  of  Per- 
manent Defences. 


ART.  I.  PRELIMINARY  CONSIDERATIONS.  PAGE 

1-4.  Permanent  fortification : its  object  and  means  of  at- 
tainment,   . . 1 

II.  GENERAL  PROFILE. 

5-7  Description  and  analysis  of  the  general  profile,  . . 2 

8.  Description  of  modern  profile, 5 

9.  Command, 5 

10.  Description  and  discussion  of  scarps,  ....  6 

11.  “ “ “ counterscarps,  . . 9 

12.  “ “ “ ditches,  ....  10 

13.  “ “ “ face  covers,  ...  11 

14.  General  remarks  on  general  profile,  ....  12 

III.  OPEN  DEFENCES. 

15.  Classes  of  open  defences, 13 

16.  Loop-holed  walls, 13 

17.  Exterior  corridors, 15 

18.  Barbette  batteries, 15 

19.  Embrasure  batteries, 16 

20.  Machicoulis  defences, 16 

IV.  COVERED  DEFENCES. 

21.  Detached  scarp  walls, . 17 

22.  Semi-detached  scarp  walls, 18 

23.  Scarp  galleries, 18 

24.  Counterscarp  galleries, 20 

25.  Bastionnets, 21 

25a.  General  remarks  on  covered  defences,  ' . . . 21 

26.  Caponniere  defences  for  the  enceinte  ditch,  . . 22 

27.  Casemates  on  land  fronts,  ......  24 


VI 


CONTEKTS. 


ART.  PAGE 

28.  Mortar  casemates, 25 

29.  Casemates  for  water  fronts, 26 

30.  Turrets, 27 

31.  Embrasures  of  casemates, 27 

32.  Bomb-proof  buildings, 28 

33.  Powder  magazines, 29 

V.  COMMUNICATIONS. 

34.  General  remarks  on  communications,  ....  30 

35.  Particular  conditions  that  communications  should  sat- 

isfy,   30 

36.  Ramps, 31 

37.  Stairs, *32 

38.  Posterns, 32 

39.  Gateway,  ....  ....  33 

40.  Portcullis  and  other  defences  of  gateway,  ...  33 

VI.  ENCEINTES. 

41.  Classes  of  enceintes, 35 

42.  Systems  and  methods  of  fortification,  . . . . 35 

43.  General  remarks  upon  systems  of  fortification,  . . 36 

VII.  OUTWORKS. 

44.  General  remarks  on  outworks, 36 

45.  General  conditions  outworks  should  satisfy, ...  37 

46.  Classes  of  outworks, 38 

47.  Covered  way, 38 

48.  ' Places  of  arms, 38 

49.  Traverses, 38 

50.  Tenaille, 39 

51.  Demi-lune, 39 

52.  Counterguard, 39 

53.  Redoubts, 40 

54.  Tenaillon, 40 

55.  Horn  work, 40 

56.  Crown  work, 40 

VIII.  ADVANCED  AND  DETACHED  WORKS. 

57,  58.  Advanced  works : definition  and  discussion,  . . 40 

59.  Detached  works : “ “ “ . . 41 

IX.  INTERIOR  RETRENCHMENTS. 

60,  61.  Interior  retrenchments  : description  and  discussion,  . 42 

62.  Cavaliers:  “ “ “ . 43 

CHAPTER  II. 

Systems  of  Fortification. 


62a.  General  considerations,  . 


44 


CONTENTS. 


Yii 


I.  BASTIONED  SYSTEM. 

ART.  PAGE 

63.  Description  and  analysis  of  the  bastioned  system,  . 44 

64.  Principal  objections  to  the  bastioned  system,  . . 45 

II.  METHODS  OF  VAUBAN. 

'65-75.  Description  of  Vaiiban’s  First  Method,  ...  46 

76.  Analysis  “ “ <<  ...  49 

III.  COEMONTAIGNE'S  METHOD. 

77-79.  Development  of  method  and  principles  applied,  . 51 

80-88.  Description  of  Cormontaigne’s  Method,  ...  53 

89.  Analysis  of  Cormontaigne’s  Method,  ....  56 

'90-94.  Use  of  the  counterguard  by  Vauban,  Cormontaigne, 

Coehoorn,  Carnot,  Haxo,  and  Noizet,  ...  57 

IV.  METHOD  OF  THE  SCHOOLS  OF  MEZIERES  AND  METZ. 

95-98.  Development  of  the  method, 58 

V.  NOIZETS  METHOD. 

‘99-104.  Description  of  Noizet’s  Method, 59 

106.  General  remarks  upon  and  objections  to  Noizet’s 

Method, 61 

107.  Modifications  adopted  or  suggested,  ....  61 

108.  Considerations  determining  the  method  to  be  selected,  62 

VI.  CHOUMARA'S  METHOD. 

109.  Principles  upon  which  it  is  based,  ....  62 

110-119.  Description  of  Choumara’s  Method,  ....  64 

120-122.  Remarks  upon  Choumara’s  Method,  ....  68 


CHAPTER  III. 

Tenailled  System. 

123.  Description  and  analysis  of  the  system,  ...  70 


CHAPTER  IV. 

Polygonal  System. 

I.  POLYGONAL  SYSTEM  IN  GENERAL. 


124.  Polygonal  system-:  description  and  analysis,  . . 71 

II.  MONT  ALEMBERT'S  METHOD. 

125.  Development  of  and  principles  involved  in  Montalem- 

bert’s  Method, 72 

126-128.  Description  of  Montalembert’s  Method,  ...  73 

129.  Modifications  introduced  by  Gen.  Brialmont,  . . 74 

130.  Polygonal  system  exemplified  by  the  defences  of  Ant- 

werp,   


74 


CONTENTS. 


viii 

CHAPTER  V. 

Existing  German  Fortifications. 

I.  RECENT  GERMAN  FORTIFICATIONS. 

ART.  page- 

131.  System  adopted, 77 

132.  General  conditions  imposed, 77 

133.  Independent  works, 78 

134.  Defensive  barracks, .78 

135.  Profiles  of  unmodified  works, 79' 

136.  Casemates, 79 

137.  Posterns, 79 

138.  Mines, 79 

139.  Powder  magazines,  guard-rooms,  store-rooms,  etc.,  . 79 

140.  Revetments,  scarps,  and  counterscarps,  ...  79 

141.  Casemates  for  cannon  and  mortars,  ....  80 

142.  Casemated  traverses, 82 

143.  Caponnieres  for  enceinte  ditch, 82 

144.  Bastionets  for  ditch  defence, 83 

145.  Details  of  defensive  barracks, 83 

146.  Remarks  upon  German  fortifications,  ....  84 

147.  Changes  required  to  fit  these  works  to  modern  re- 

quirements,   85 

II.  FRONTS  OF  POSEN. 

148-151.  Outline  description  of  front, 86 

III.  FORT  ALEXANDER  AT  COBLENTZ. 

152-158.  Description  of  Fort  Alexander, 88- 

159-162.  Remarks  upon  the  polygonal  system  as  applied  by 
the  Germans,  with  analysis  of  the  relative  advan- 
tages and  defects  of  the  polygonal  and  bastioned 
systems, 90' 

163.  Recent  modifications  in  the  bastioned  and  polygonal 

systems, 92 

164.  Considerations  determining  the  character  of  future 

fortifications  and  systems  to  be  adopted,  . . 92^ 

CHAPTER  VI. 

Detached  Forts. 

165.  Now  the  main  line  of  defence, 94 

166.  Trace  adopted  ; dimensions ; garrison  ; armament ; 

profiles  and  revetments, 94 

167.  Bomb-proof  covers  and  use  of  turrets,  ....  95 

168.  Communications,  . 95 

169.  Small  but  important  works  entirely  bomb-proof,  . . 96 

170.  Outworks, 96 

171.  Glacis  or  wing  batteries, 96 

172.  Intermediate  works, 96. 


CONTENTS. 


IX 


CHAPTER  VII. 

Influence  of  Irregularities  of  Site  on  the  Forms  and  Com- 
binations OF  THE  Elements  of  Permanent  Works. 

ART.  PAGE 

178-175.  General  conditions  to  be  satisfied,  ....  97 

176.  Conditions  of  command, 98 

177, 178.  Rule  to  be  observed  in  adaptation  of  plan  to  site,  . 98 

179.  Remarks  upon  foregoing  subjects,  ....  100 

II.  DEFILEMENT  OF  PERMANENT  WORKS. 

180.  Remarks  upon  defilement  of  permanent  works,  . . 101 

181.  Data  for  the  “ “ “ “ . . 102 

182-185.  Limits  of  defilement, 103 

186.  Dangerous  zones  of  the  site, 104 

187.  Portions  of  zones  that  may  be  disregarded,  . . . 104 

188.  Defilement  of  masonry, 104 

189.  Limits  of  defilement  for  small  works,  ....  104 

190.  Front  and  lateral  limits, 104 

191.  Remarks, 105 

III.  PROBLEMS  OF  DEFILEMENT. 

192.  Cases  of  defilement, 105 

193.  Front  defilement  of  a redan,  the  command  being 

given, 106 

194.  Reverse  defilement  of  a redan, 108 

195.  Position  of  traverse  for  reverse  defilement,  . . . 109 

196.  Forms  and  arrangement  of  traverses,  ....  109 

197.  Combinations  of  several  traverses,  ....  109 

198.  Precautions  to  be  taken  in  locating  traverses,  . . 110 

199.  Remarks  upon  defilement  by  traverses,  . . . 110 

200.  General  case  of  the  defilement  of  a bastion,  . . . 110 

201.  Defilement  of  retired  from  advanced  works,  . . 112 

202.  Defilement  by  parados  and  conclusions  drawn  from 

experiments, 112 

203.  General  remarks  upon  defilement— Recapitulation,  . 113 


CHAPTER  VIII. 

Accessory  Means  of  Defence. 

I.  WATER  AS  AN  ACCESSORY. 

204,  205.  Marshy  sites, 115 

206.  Artificial  inundations, 115 

207.  Water  applied  as  an  active  means  of  defence,  . , 116 

II.  OTHER  MATERIALS  AS  ACCESSORIES. 

208.  Natural  and  artificial  beds  of  rock  as  an  accessory,  . 116 

209.  Stumps  of  trees  as  an  obstmction, .....  117 

210.  “ Obstacles”  as  an  accessory, 117' 


X 


CONTENTS, 


III.  MINES  AS  ACCESSORIES. 

ART.  PAGE 

211.  General  considerations  in  their  use,  . , , .117 


CHAPTER  IX. 

Sea-coast  Defence. 

I.  BATTERIES  ON  LAND. 

212.  General  conditions  of  sea-coast  defence,  . . . 118 

213.  Use  of  stone  casemates  abandoned,  ....  118 

214-217.  Earthen  batteries, ,118 

218-221.  Disappearing  gun  carriages, liJ 

222-224.  Use  of  traverses, 120 

225.  Gun  pits, 120 

226, 227.  Mortar  batteries, 120 

228.  Batteries  on  elevated  sites,  . . . . . . 121 

229,  230.  The  use  of  armor, • . .121 

II.  FLOATING  BATTERIES. 

231.  Conditions  requiring  their  use, 121 

III.  OBSTACLES,  SUBMARINE  MINES,  AND  TORPEDOES. 

232.  Their  use  a necessity  in  the  defence  of  harbors,  . . 122 

233.  General  considerations  to  be  fulfilled  by  passive  ob- 

stacles,   122 

234.  Different  kinds  of  passive  obstacles,  ....  122 

235.  First  use  of  submarine  mines  and  torpedoes,  . . 123 

236.  General  conditions  to  be  fulfilled  by  submarine 

mines,  .........  123 

237-239.  Uses  of  submarine  mines  and  torpedoes,  . . . 123 

240-244.  Classification  and  general  description  of  submarine 

mines,  124 

245.  Conditions  to  be  fulfilled  by  the  electrical  system,  . 125 

246,  247.  Construction  of  mine  cases, 125 

248.  Explosives  used, 125 

249.  Movable  torpedoes,  general  description,  . . . 125 

250.  Destructive  range  of  submarine  explosions,  . . . 125 

251-255.  Organization  of  fortifications,  mines,  and  torpedoes 

for  the  defence  of  harbors, 126 

256.  Remarks, 127 


CHAPTER  X. 

The  Defensive  Organization  of  Frontiers  with  Permanent 
Fortifications. 

257.  Opinions  held  by  prominent  military  authorities  on  the 

necessity  of  fortified  frontiers,  ....  128 

258.  Remarks  on  the  organi^tion  of  the  frontier  defences 

of  the  United  States, 


129 


CONTENTS.  Xi 

ART.  PAGE 

259.  Important  points  to  be  fortified, 130 

260.  Rivers  and  mountain  ranges  as  natural  defensive 

lines 130 

261.  Advantages  offered  both  in  defensive  and  offensive 

operations  by  fortified  points  on  rivers,  . . .131 

262.  Points  to  be  fortified  in  mountain  ranges,  . . . 131 

263.  Defensive  means  adopted  for  the  coasts  of  the  United 

States, 131 

264.  Character  of  the  works  necessary  for  sea-coast  de- 

fence,   132 

265.  Defences  for  important  commercial  marts  and  naval 

depots, 132 

266.  Defence  of  important  extensive  roadsteads,  . . . 134 

267.  Opinions  entertained  by  foreign  military  authorities 

on  the  fortification  in  a permanent  manner  of  im- 
portant inland  centres  of  population,  . . . 134 

268.  Fortifications  of  Paris  and  Lyons  in  France,  . . 135 

269.  Objections  to  the  adoption  of  European  practice  for 

the  defences  of  the  large  cities  of  the  United 
States, 135 


CHAPTER  XL 

Summary  of  the  Progress  and  Changes  op  Fortification. 

I.  PROGRESS  OF  THE  DEFENCE. 

270.  Fortification  as  seen  in  its  earliest  stages,  . . .137 

271.  Enclosures  of  simple  stone  walls  and  towers,  . . 137 

272.  Insufficiency  of  these  against  improved  means  of  of- 

fence,   138 

273.  Introduction  of  ditches  and  wide  ramparts  as  defen- 

sive features, 138. 

274.  Examples  of  the  great  strength  and  extent  of  some 

ancient  fortifications, 139 

275.  Methods  of  attack  used  by  the  Ancients,  . . . 139 

276.  Defensive  methods  employed  by  the  Ancients,  . . 14(1 

277.  Rise  and  fall  of  the  art  under  the  Romans,  . . . 140 

278.  Progress  of  the  art  under  the  Western  Empire,  . . 141 

279.  Conditions  of  the  art  under  the  Feudal  System,  . . 141 

280.  Castellated  fortifications  of  the  Feudal  Period,  . . 142 

281.  Fortifications  of  cities  during  the  same  period,  . . 142 

282.  Changes  in  the  art  occasioned  by  the  invention  of 

gunpowder, 143 

283.  First  appearance  of  the  bastioned  system  and  the 

changes  consequent  upon  it, 143 

284.  Italian  school  of  engineers, 144 

285.  Spanish  school, 145 

286.  Dutch  school, 145 

287.  German  school, 146 

288.  Swedish  school, ' , , . 146 

289.  French  school, 147 


Xll 


CO^^TENTS. 


II.  PROGRESS  OF  THE  ATTACK  SINCE  THE  INVENTION  OF 
FIREARMS. 

ART.  PAOE 

290.  Methods  and  progress  of  the  attack  from  the  inven- 

tion of  gunpowder  to  the  time  of  Vauban,  . . 148 

291.  Changes  and  improvements  made  in  the  methods  of 

attack  by  Vauban, 149 

292.  Present  condition  of  the  art  in  the  United  States,  . . 150 

293.  Probable  changes  in  the  immediate  future,  . . . 151 


CHAPTER  XII. 

Modern  Constructions  in  Iron  and  Steel. 

294.  Introduction  of  armor, 152 

295.  Its  development, 152 

:296-299.  Its  behavior  under  impact  and  relative  cost,  . . .153 

300.  Application  of  armor  to  land  defences  comparatively 

free  from  difficulties, 154 

301.  English  armored  forts, 154 

302.  English  turrets, 155 

303, 304.  Dover  turret,  155 

305, 306.  French  turret  (Mougin), 155 

307,  308.  German  turret  (Schumann), 156 

309.  Competitive  trials  of  French  and  German  turrets,  . 157 

310.  Revolving  turret  caponier, 158 

311.  Fixed  turret  caponier, . 158 

312.  Disappearing  turret, 159 

313.  Cost  of  small  turrets, 159 

314.  Application  of  small  turrets, 159 

315.  Griison  casemates, 160 


APPENDIX  I. 

Penetration  of  Projectiles  and  Thickness  op  Parapets. 

Formulas  for  penetration  in  iron,  . • , . . . .161 

Calculated  penetration  into  clay,  sand,  and  granite,  . , . 162 

Actual  penetrations  into  earth,  granite,  concrete,  etc.,  . . 163 

Prescribed  thicknesses  of  German  parapets,  ....  164 


APPENDIX  II. 

Frontier  and  interior  fortifications  of  France,  Germany,  Italy, 

Austria-Hungary,  and  Russia  in  Europe,  ....  165 


APPENDIX  III. 


Books  of  reference. 


170 


CONTENTS. 


XIU 


LIST  OF  PLATES. 


Plate  No.  1.  Typical  modern  profiles, 

“ 2.  Mortar  battery. 

“ 3.  Profiles  of  older  forts. 

4.  Scarps,  counterscarps,  and  galleries. 

**  5.  Sea-coast  fronts,  caponniere  and  bastionet. 

**  6.  Sea-coast  and  land-front  casemates. 

**  7.  Barbette  battery  and  disappearing  gun-carriages. 

**  8.  Machicoulis,  posterns,  Totten  embrasures,  and  outline 

plans  of  ditferent  systems  of  fortification. 

**  9.  Outworks. 

10.  Vauban  and  Cormontaigne’s  fronts. 

11.  Brialmont’s  method. 
lla.Noizet’s  front, 

12.  Choumara's  method. 

“ 13.  Montalembert  and  Carnot’s  methods. 

14.  Fort  Alexander  and  front  of  Posen. 

**  15.  T^te  de  pont  opposite  Germersheim. 

**  16.  Detached  work  (German). 

**  17.  Problems  of  defilade. 

**  18.  English,  French,  and  German  turrets. 

**  19.  Disappearing  turrets,  fixed  and  revolving  iron  capo- 


Frontispiece — Griison  chilled  iron  casemated  battery  near  Antwerp. 


ELEMENTS 


OF 

PERMANENT  FORTIFICATION. 


CHAPTEK  L. 

PRELIMINARY  CONSIDERATIONS  AND  COMPONENT 
ELEMENTS  OF  PERMANENT  DEFENCES. 

I. 

PRELIMINARY  CONSIDERATIONS. 

1.  The  iQvm  per7ncme7it  fortification  is  applied  to  those 
defences  which,  constructed  of  materials  of  a durable  nature 
and  designed  for  permanent  occupancy  by  troops,  receive 
such  a degree  of  strength  that  an  enemy  will  be  forced  to 
the  operations  either  of  a siege  or  a blockade  to  gain  pos- 
session of  them. 

2.  These  defences  differ  from  temporary  fortification  but 
in  degree ; the  general  principles  of  defensive  works  being 
alike  applicable  to  both. 

3.  The  object  of  such  defences  is  to  secure  the  permanent 
military  possession  of  those  points,  either  on  the  frontiers 
or  in  the  interior  of  a state,  which  must  at  all  times  have  a 
well-defined  bearing  on  the  operations  of  a defensive  or  an 
offensive  war. 

4.  For  the  attainment  of  this  object  the  following  gen- 
eral conditions  should  be  fulfilled  in  the  arrangement  of 
such  defences : 

1st.  Tlteij  should  he  of  s^ifiicient  strength  to  resist  with 
success  all  the  ordhiary  means  resorted  to  hy  an  assailant 
in  an  open  assault. 

2d.  Be  p7^ovided  with  suitable  shelters  to  protect  the 
troops,  the  armament^  and  the  7nagazines  of  provisions  and 
mimitions  of  war  7'equired  for  their  defence  against  the 
destructive  measures  of  the  assailant. 

1 


2 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


3d.  Be  so  planned  that  every  point  exterior  to  the  de- 
fences within  cannon  range  shall  he  thoroughly  swept  hy 
their  fire. 

4 th.  Have  secure  and  easy  means  of  communication  for 
the  movement  of  the  troops.,  both  within  the  defences  and  to 
the  exterior. 

5th.  And^  finally,  he  provided  with  all  stcch  accessory 
dfiensive  means  as  the  natural  features  of  the  position  it- 
self may  afford,  to  enable  the  garidson  to  dispute  with  en- 
ergy the  occupancy  hy  the  assailant  of  every  point  both 
vyithin  and  exterior  to  the  defences. 

The  defensive  brancli  of  the  military  engineer’s  art  con- 
sists in  the  knowledge  of  the  means  which  are  employed  to 
fulfil  the  above  conditions,  and  of  their  suitable  adaptation 
to  the  natural  features  of  the  positions  he  may  be  called 
upon  to  fortify. 


II. 

COMPONENT  ELEMENTS  OF  PERMANENT  WORKS. 

GENERAL  PROFILE. 

5.  The  first  condition  laid  down  for  permanent  defences, 
security  from  open  assault,  supposes  a strength  of  profile 
greatly  superior  to  that  which  is  given  to  temporary  works. 

6.  The  usual  and  most  simple  form  of  profile  for  perma- 
nent works  consists  of  a rampart.,  a parapet.,  and  a ditch., 
exterior  to  which  a glacis  is  usually  throwm  up. 

The  Rampart,  a.  Plates  1 and  3,  is  an  earthen  mound, 
raised  above  the  natural  level  of  the  ground,  and  upon 
which  the  parapet  b is  placed. 

The  rampart  thus  serves  to  give  the  troops  and  arma- 
ment, which  are  placed  on  top  of  it  and  behind  the  parapet, 
a commanding  view  over  the  ground  to  be  guarded  by  the 
fire  of  the  defences;  whilst  at  the  same  time  it  increases 
the  ol)stacle  to  an  open  assault  by  the  additional  height  it 
gives  to  the  scarp. 

The  top  surface  of  the  rampart,  b c,  in  rear  of  the  parapet, 
termed  the  terre-plein.  affords  the  troops  and  armament  a 
convenient  position  for  circulation  from  point  to  point, 
where  they  are  sheltered  from  the  direct  view  of  the  assail- 
ant. 

The  rampart  is  usually  terminated  on  the  interior,  a b,  by 


ELEME^q’TS  OF  PERMANE^^T  FORTIFICATION'. 


3 


•allowing  tlie  earth  to  assume  either  its  natural  slope,  or  one 
somewhat  less  steep,  termed  the  ramjpart-slope. 

In  cases  where  this  slope  would  take  up  too  much  of  the 
ground  within  the  defences  it  is  replaced  bj  a wall,  termed 
the  which  rises  from  the  level  cf  the  interior 

ground,  termed  t\\Q  parade^  to  the  interior  line  of  the  terre- 
plein. 

Inclined  planes  of  earth,  termed  ramps^  lead  from  the 
parade  to  the  terre-plein,  and  serve  as  communications  be- 
tween them. 

7.  The  Parapet,  b,  PL  3,  Fig.  4,  serving  the  same  pur- 
poses in  permanent  as  in  field  works,  receive  the  same  gen- 
eral form  as  in  the  latter. 

The  essential  properties  of  the  parapet,  as  in  field- wmrks, 
are  to  afford  cover  from  the  enemy’s  missiles,  and  every 
facility  for  sweeping  his  positions  by  the  fire  of  its  artillery 
and  small-arms. 

To  afford  perfect  cover  against  direct  fire,  at  short  range,  a 
thickness  of  parapet  equal  to  once  and  a half  the  penetration 
of  the  gun  brought  against  it  is  usually  used.  (For  penetra- 
tions, see  Appendix  I.)  It  is  not  ahvays  practicable  to  give 
tliis  full  thickness,  nor  is  it  in  the  general  case  necessary, 
since  the  penetration  of  elongated  projectiles  into  parapets 
■of  the  usual  form  is  less  than  into  experimental  butts.  The 
projectile  will  generally  be  deflected  from  its  direct  course, 
turn  upward,  and  pass  out  from  the  superior  slope  before 
passing  through  the  parapet.  These  considerations  have  led 
the  German  engineers  to  give  to  the  parapets  of  their  new 
inland  forts,  Plate  1,  Figs.  1 and  3,  a thickness  varying  from 
IT  to  23  feet,  and  to  sea-coast  wmrks  40  feet. 

. The  French  consider  20  to  26  feet  necessary  for  land 
fronts,  and  our  own  engineers  have  recommended  in  special 
cases  TO  feet  thickness  in  sea-coast  batteries.  The  most  of 
the  parapets  of  existing  works  have  received  only  from  18 
to  20  feet,  and  these  will  doubtless  be  found  to  give  efficient 
cover  against  any  ordinary  attack. 

In  small  works  of  less  importance  and  not  liable  to  be 
breached  the  thickness  may  be  reduced  to  12  or  15  feet. 

In  some  cases  the  exterior  slope,  PI.  3,  Fig.  12,  is  replaced 
by  a wall,  wdiich,  resting  on  the  top  of  the  scarp  wall,  rises 
to  the  level  of  the  superior  slope. 

The  exterior  slope  of  the  parapet  usually  rises  from  the 
top  of  the  scarp  wall,  leaving  a narrow  berm  between  it  and 
the  scarp,  or  face  of  the  w'all. 

In  some  cases,  however,  it  is  thrown  so  far  to  the  rear  of 


4 


ELEMENTS  OF  PEKMANENT  FOKTIFICATION. 


the  scarp,  PI.  1,  Figs.  2 and  5,  as  to  leave  sufficient  room' 
for  a communication  c,  in  front  of  the  parapet,  in  which  the 
troops  can  circulate  under  cover  from  fire,  being  masked 
either  bv  an  earthen  parapet,  or  by  a wall,  n.  This  covered 
communication,  c,  is  termed  an  exterior  corridor  or  chemin- 
de-ronde. 

For  the  superior  slope,  the  rule,  so  long  in  use,  of  making 
it  six  base  to  one  perpendicular,  or  is  still  generally  fol- 
lowed. 

This  rule  has  not  been  adopted  because  cannon  cannot  be 
fired  under  a greater  depression  than  although,  from  the 
inconveniences  attending  greater  depressions  than  this,  artil- 
lerists are  unwilling  to  resort  to  them  ; but  from  a greater 
depression  necessitating  the  employment  of  very  deep  em- 
brasures, or  else  that  of  platforms  raised  so  high  to  the  rear 
that  the  men  serving  the  guns  will  be  very  much  exposed 
to  fire. 

Still,  where  a greater  or  less  plunge  is  necessary  to  bring 
the  exterior  ground  better  under  fire  it  should  be  adopted, 
as  it  is  to  be  observed  that  the  strength  of  the  parapet  at 
the  angle  of  the  interior  crest  should  be  increased  where  the 
assailant  can  have  a plunging  fire  on  it ; whereas  when  ex- 
posed to  a fire  from  a level  much  below  this  crest  the  angle 
at  it  will  be  less  exposed,  and  the  plunge  of  the  parapet  can 
be  increased  without  injury. 

Until  within  a recent  period,  the  interior  slope,  the  ban- 
quette, and  banquette  slope  received  the  same  forms  and 
dimensions  as  in  field  works  ; the  top  of  the  rampart  falling, 
from  the  foot  of  the  banquette  slope  to  the  crest  of  the  ram- 
part slope,  one  foot,  to  drain  off  the  surface-water. 

In  the  later  profile  the  interior  slope  is  and  has  a baiu 
quette  tread  of  only  2 feet,  with  a banquette  slope  of  only 
Where  guns  are  mounted  either  in  barbette  or  embrasure 
the  interior  slope  is  increased  to  -J,  and  the  banquette  and  its 
slope  removed  ; the  earth  taken  off  by  these  modifications 
serving  to  form  the  merlons  between  the  shallow  embrasures 
cut  into  the  parapets. 

When  the  foot  of  the  exterior  slope  rests  on  the  top  of 
the  scarp  wall,  a berm  of  two  feet  in  breadth  is  left  between 
it  and  the  edge  of  the  coping.  This  breadth  of  berm  is 
objectionable,  as  giving  a good  landing-place  for  a scaling- 
party  in  an  open  assault ; and  it  is  proposed,  when  the  work 
is  in  danger  of  an  attack,  to  reduce  the  berm  to  18  inches  or 
one  foot,  by  increasing  the  thickness  of  the  parapet  0 inches, 
or  one  foot. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


5 


The  exterior  slope,  for  the  reasons  given  in  discussing  the 
parapets  of  field-works,  should  not  be  greater  on  land  fronts 
than  the  natural  slope  of  the  earth  of  which  the  parapet  is 
formed. 

8.  The  profiles  now  used  are  shown  in  Plate  1,  Figs.  1,  2, 
3,  4.  and  5.  The  part  of  the  terre-plein  used  as  a general 
barbette  for  heavy  guns  has  a width  and  height  suitable  for 
the  carriages  used ; that  used  as  a road  in  rear  is  given  a 
breadth  sufficient  for  communication  (20  to  25  feet),  and  is 
placed  low  enough  to  be  screened  from  a trajectory  falling 
at  an  angle  of  i,  if  this  is  consistent  with  a sufficient  cover 
over  the  arches  of  the  bomb-proofs. 

In  the  older  works  the  terre-plein  received  a breadth  of  40 
to  50  feet,  estimated  between  the  interior  crest  and  the  top 
of  the  rampart  slope.  From  motives  of  economy,  and  some- 
times to  enlarge  the  parade,  this  breadth  was  reduced  to  20 
or  24  feet,  and  a parade  wall  substituted  for  the  rampart 
slope.  The  great  length  of  modern  guns  and  the  necessity 
for  increased  room  for  bomb-proofs  under  the  terre-plein 
have  caused  a return  to  a greater  width.  The  minimum  is 
now  about  40  feet. 

The  great  command  and  low  scarps  of  modern  works 
make  the  exterior  slope  much  longer  than  it  formerly  was. 
It  is  sometimes  broken  up  by  introducing  two  or  more  berms 
between  its  crest  and  foot. 

9.  The  command^  or  height  of  the  parapet  above  the  site, 
has  a very  important  bearing  in  the  close  defence  of  perma- 
nent works. 

In  the  first  place,  the  greater  the  command,  the  greater 
will  be  the  plunge  of  the  guns  on  the  exterior  ground,  and 
the  more  difficulty  wdll  the  assailant  meet  with  in  obtaining 
cover  in  his  trenches  from  this  plunge  ; being  obliged  to 
make  them  deeper  than  usual,  and  to  increase  the  height  of 
their  parapets. 

In  the  second  place,  having  to  fire  under  greater  angles 
of  elevation,  as  the  command  is  greater,  he  will  only  be  able 
to  reach  the  terre-pleins  by  the  use  of  diminished  charges 
and  a corresponding  decrease  in  accuracy  of  fire.  For 
defence  against  the  distant  attack  by  long-range  guns  these 
considerations  have  less  weight,  the  advantage  of  command 
in  this  case  arising  principally  from  its  giving  a better  view 
of  the  enemy’s  works. 

Motives  of  economy,  however,  require  the  command  to 
be  restricted  within  quite  narrow  limits.  When  the  w^ork 
consists  of  a simple  enceinte  enveloped  by  a covered-way 


6 ELEMENTS  OF  PERMANENT  FORTIFICATION. 

the  command  may  be  reduced  to  16  feet,  which  allows  a 
sufficient  command  above  the  glacis  crest.  The  height  of 
the  latter  is  so  fixed  that  a projectile  falling  at  an  angle  of 
J and  just  grazing  it  shall  not  strike  the  scarp  wall  at  a 
distance  less  than  sixteen  feet  above  its  bottom. 

10.  Scarp. — Scarp  walls  full ^ detached,  or  semi-de- 

tached. A full  scarp  wall  is  a retaining-wall  extending 
from  the  bottom  of  the  ditch  to  the  foot  of  the  exterior 
slope,  which  rests  upon  its  top  (Plate  3,  Figs.  2 and  4). 

A detached  scarp  wall  (Plate  1,  Figs.  1,  2,  and  3)  rises 
from  the  bottom  of  the  ditch,  leaving  between  its  back  and 
the  foot  of  the  rampart  behind  it  a breadth  of  several  feet, 
either  on  the  same  level  as  the  bottom  of  the  ditch,  or  raised 
a few  feet  above  this  level.  In  some  cases  the  wall  is  built 
with  several  tiers  of  arched  recesses  on  its  back,  the  por- 
tions of  the  wall  in  front  of  which  are  pierced  with  loop- 
holes, each  recess  being  of  sufficient  size  to  give  shelter  to 
several  men  serving  the  loop-holes,  and  tiring  into  the  ditch 
and  on  the  top  of  the  counterscarp. 

A semi-detached  scarp  wall  (Plate  1,  Fig.  5)  has  its  lower 
portion  made  as  retaining-wall,  generally  built  with  reliev- 
ing arches,  either  closed  or  open  in  rear ; the  upper  portion 
for  a height  from  8 to  12  feet  being  detached  from  the  ram- 
part and  prepared  for  defence  like  the  preceding  example. 

Detached  and  semi-detached  scarp  walls  have  evident 
advantages  over  the  full  scarp.  They  are  better  covered 
by  the  glacis  from  the  plunging  fire  of  the  assailant ; they 
offer  the  same  obstacle  to  an  escalade  as  the  latter,  and 
when  the  assailant  has  gained  the  top  of  the  wall  they 
present  the  hurther  difficulty  of  his  getting  down  on  the 
other  side  ; they  give  a good  fire  upon  the  ditch,  and  are 
thus  favorable  to  the  safety  of  sortie  parties  in  retreat ; 
and  when  a wide  space  is  left  between  them  and  the  para- 
pet, room  is  afforded  for  the  formation  of  a column  on  each 
side  of  any  breach  made  in  the  wall,  to  charge  in  flank  an 
assaulting  column  entering  the  breach. 

On  the  other  hand,  these  walls  favor  an  assaulting  column 
rushing  through  a breach  in  them,  as  the  assailants  can 
spread  along  the  corridor  on  the  right  and  left,  and  assault 
tlie  work  on  a wider  front.  Should  the  assailant  not  choose 
this  course,  he  has  the  alternative  of  establishing  himself 
securely  upon  the  exterior  slope  in  trenches ; and  if  it  suits 
his  purposes  better,  to  drive  a mine  gallerv  from  the  breach 
into  the  rampart,  to  blow  it  up  and  open  a breach  into  the 
work. 


ELEMENTS  OF  PERMAXEXT  FORTIFICATION^. 


7 


But  a very  marked  defect  in  all  of  these  detached  scarps 
is  the  exposed  condition  in  which  the  men  behind  them  are 
from  the  splinters  from  the  walls  when  the  corridor  can  be 
enfiladed,  and  from  the  splinters  of  exploding  shells,  which 
either  lodge  and  explode  in  the  rampart,  or  roll  down  it  and 
explode  in  the  corridor. 

To  break  in  some  measure  the  effects  of  this  enfilade,  and  . 
also  to  prevent  an  assaulting  column  from  spreading  to  the 
right  and  left  along  the  corridor,  traverse  walls,  having 
doors  in  them  for  communication  and  loop-holed  to  fire 
along  the  corridor,  are  placed  from  point  to  point,  running 
from  the  scarp  wall  back  to  the  exterior  slope  across  the 
corridor.  But  these  cross-walls  would  soon  be  destroyed 
by  an  ordinary  enfilade,  and  the  splinters  from  them  would 
render  the  corridor  untenable. 

J^otwithstanding  this  defect,  on  account  of  their  many 
advantages,  detached  and  semi-detached  walls  are  now  very 
generally  adopted  by  engineers.  Since  their  object  is  to 
prevent  escalade  and  stop  assaulting  columns  and  lines,  they 
would  ordinarily  only  be  manned  by  the  defenders  when 
the  assailants  were  so  close  to  them  as  to  preclude  the  use 
of  their  artillery  against  the  defence. 

In  order  to  protect  dry  ditches  against  escalade  a scarp 
wall  30  feet  high  was  until  recently  considered  necessary. 
This  height  had  been  established  from  long  experience  in 
sieges  preceding  the  introduction  of  the  breechdoading  small 
arms  and  metallic  ammunition.  With  the  increased  rapid- 
ity of  fire  resulting  from  these  improvements,  and  machine 
guns,  engineers  are  all  of  the  opinion  that  a less  height  will 
now  afford  ample  security. 

The  French  engineers  consider  the  maximum  height  nec- 
essary for  full  scarps  for  main  works  to  be  from  23  to  26 
feet,  and  for  outworks  from  16  to  20.  With  detached 
scarps  they  reduce  these  heights  to  20  feet  for  the  main 
work  and  16  or  even  13  for  the  outworks.  The  German 
and  Belgian  engineers  adopt  about  the  same  heights. 

Some  engineers  have  shown  a tendency  to  do  away  with 
either  the  revetted  scarp  or  counterscarp,  and  in  some  in- 
stances with  both;  trusting  to  entanglements  and  other 
obstacles  combined  with  the  fire  of  the  work  to  repel 
assault. 

While  these  means  may  be  sutficient  in  works  fully  gar- 
risoned and  protected  against  surprise  by  constant  watch- 
gulness,  a restriction  to  their  use  would  be  fraught  with 
freat  danger  to  works  having  small  garrisons  if  suddenly 


8 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


attacked,  and  would  add  greatly  to  the  fatigue  of  the  de- 
fence by  the  additional  guard  duty  and  the  constant  state 
of  readiness  to  repel  assault  required  of  the  garrison.  As 
the  object  of  all  fortifications  is  to  compensate  for  numeri 
cal  weakness  on  the  part  of  the  defence,  the  safer  practice 
would  seem  to  be  to  do  this  by  placing  such  an  obstacle  in 
the  way  of  an  open  assault  that  but  a few  men  promptly 
availing  themselves  of  it  might  hold  back  the  assailant 
until  a sufficient  force  could  be  gathered  at  the  point  as- 
sailed to  render  the  attack  abortive. 

Besides  securing  the  place  from  an  escalade,  full  and 
semi-detached  scarp  walls  act  as  retaining-walls,  to  hold  up 
the  excavated  side  of  the  ditch  towards  the  rampart,  the 
rampart  itself,  and  the  parapet.  This  requires  that  they 
should  receive  a thickness  and  form  of  profile  adapted  to 
this  end. 

The  top  stone  of  the  wall,  k,  PI.  3,  Fig.  4,  termed  the 
cordon  or  coping^  projects  beyond  its  face,  and  serving  as 
a larmier  or  drip^  protects  it  from  the  effects  of  the  rain- 
water, which  runs  from  the  parapet  upon  die  coping. 

The  line  in  which  the  face  of  the  scarp  wall  if  prolonged 
would  intersect  the  coping  is  termed  the  magistral.  This 
is  a very  important  line  in  drawing  the  plans  of  permanent 
works,  serving  as  the  directing  line  to  fix,  both  upon  the 
drawing  and  upon  the  ground  in  setting  out  the  work,  the 
dimensions  and  relative  positions  of  all  the  bounding  lines 
of  the  parapet  and  other  parts. 

Although  no  ordinary  scarp  walls  can  resist  breaching, 
and  have  to  be  covered  by  earthen  masks  to  screen  them 
from  the  distant  fire  of  the  assailed,  they  should  be  so  con- 
structed as  to  render  breaching  a difficult  operation  ; limit- 
ing the  breach  made  to  the  part  of  the  wall  actually  de- 
stroyed by  the  assailant’s  projectiles. 

In  the  scarp  walls  of  Yauban  and  Cormontaigne,  and  in 
many  of  the  more  modern  fortifications  of  Europe,  the  scarp 
walls  are  built  solid,  with  counterforts  on  their  back,  of  the 
forms  and  dimensions  adopted  by  Yauban.  This  engineer 
gave  his  scarps  a thickness  of  about  i their  height  and  a 
batir  of  Cormontaigne,  finding  that  the  faces  of  these 
walls  w^ere  soon  injured  by  the  weather,  adopted  a batir  of 
This  for  the  same  reason  was  increased  by  some  to 
by  others  to  ^ ? ^ind  in  our  climate,  where  the  action  of 
the  weather  on  masonry  is  very  injurious,  our  engineers 
have  varied  their  batir  from  to 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


9 


To  give  greater  efficacy  to  the  resistance  offered  to 
breaching,  and  to  prevent  the  breach  from  taking  a gentle 
slope  when  formed,  it  has  been  proposed  by  some  to  back 
the  wall  and  counterforts  by  a kind  of  pise  work,  or  with 
beton  with  but  little  lime  in  it,  of  several  feet  in  thickness. 

Others  have  proposed,  for  the  same  purpose,  to  connect 
the  end  of  the  counterforts  by  vertical  arches,  and  to  fill  the 
cells  thus  formed  either  with  pise,  or  with  this  poor  beton. 

Others  prefer  long  thin  counterforts  sustaining  several 
tiers  of  relieving  arches;  the  cells  thus  formed  being  left 
open  for  defence,  for  bomb-proof  shelters,  and  for  maga- 
zines for  provisions,  etc. 

All  these  expedients  have  been  tried,  though  not  fully 
tested  by  experiment;  the  last  under  all  points  of  view  hav- 
ing the  most  advantages  in  its  favor. 

11.  Counterscarp  Wall.  A revetted  counterscarp  is 
regarded  as  adding  to  the  difficulty  of  descending  into  the 
ditch,  and  as  offering  greater  security  against  an  open 
assault.  For  this  purpose  the  wall  should  not  be  less  than 
12  or  15  feet  in  height  to  offer  a serious  impediment ; in  any 
case,  where  motives  of  economy  do  not  imperiously  forbid 
it,  the  counterscarp  wall  of  the  enceinte  should  be  from  18 
to  24  feet  in  height.  This  height  will  not  only  give  great 
security  to  the  ditch,  but,  as  will  be  seen  in  the  description 
of  the  siege  works  of  the  assailant,  it  will  delay  considerably 
his  progress,  as  the  gallery  by  which  he  must  generally 
reach  the  bottom  of  the  ditch  from  the  level  of  the  covered- 
way terre-plein  is  one  of  the  slowest  and  most  laborious  of 
his  operations. 

Besides  giving  greater  security  against  a surprise,  a 
revetted  counterscarp  enables  the  assailed  to  circulate 
through  the  ditches  even  when  the  assailant  has  established 
his  trenches  along  the  glacis  crest,  as  the  top  of  the  counter- 
scarp wall  will  screen  the  troops  passing  along  the  bottom 
of  the  ditch. 

It  also  affords  facilities  for  forming  a counterscarp  gallery 
behind  it  loop-holed  for  the  defence  of  the  ditch  against  an 
open  assault,  which  for  small  worhs  without  thorough 
fianking  arrangements  will  he  found  very  serviceable. 

Besides,  this  gallery" will  be  found  of  great  utility  where  a 
system  of  defensive  mines  is  to  form  a part  of  the  defences. 

But  as  counterscarp  galleries,  if  seized’  upon  by  the 
assailant,  may  be  turned  against  the  defences,  it  is  impor- 
tant that  they  should  be  placed  in  positions  where  they  will 
be  of  little  value  to  the  assailant  if  seized  upon. 


10 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


The  necessity  for  revetting  with  a wall  of  masonry  the 
scarp  and  counterscarp  of  a wet  ditch  in  which  the  water 
can  be  retained  at  a level  of  six  feet  in  depth,  is  not  so 
obvious,  as  when  the  ditch  is  wide  the  obstacle  of  the  water 
alone  would  seem  to  be  sufficient  to  secure  the  place  from  a 
surprise.  Many  works  under  this  condition  have  been  built 
with  simple  earthen  scarps  and  counterscarps;  in  some 
instances  a chemin-de-ronde  being  formed  by  leaving  a wide 
l)erm  between  the  foot  of  the  exterior  slope  and  the  crest 
of  the  scarp,  and  planting  a loop-holed  stockade  near  the 
crest. 

But  in  rigorous  climates,  where  the  water  freezes  hard,  a 
wet  ditch  is  no  longer  a security  in  winter ; and  a dry  ditch 
with  the  usual  revetted  scarp  and  counterscarp  is  a better 
security  against  a surprise  than  the  expedients  proposed,  of 
keeping  an  open  channel  along  the  middle  of  the  ditch  of 
12  feet  in  width,  piling  up  on  each  side  ot  it  the  ice  taken 
from  the  channel  and  throwing  water  over  the  exterior 
slopes  to  freeze  and  form  a slippery  surface  to  an  assaulting 
column. 

12.  Ditch.  The  width  and  depth  of  the  enceinte  ditch 
depend  mainly  upon  the  amount  of  embankment  required 
for  the  enceinte  and  the  glacis,  and  therefore  will  result 
from  the  calculation  for  equalizing  the  excavation  and  em- 
bankment which  these  demand. 

A deep  and  narrow^  ditch  offers  the  advantage  of  present- 
ing more  difficulty  to  the  assailant  in  reaching  the  bottom 
of  it,  either  in  an  open  assault,  or  by  a gallery  in  the  attack 
by  regular  approaches,  thus  prolonging  the  defence. 

It  masks  better  the  sally-ports  from  the  enemy’s  fire  by 
allowing  them  to  be  placed  so  low  that  the  projectiles  com- 
ing over  the  glacis  cannot  reach  them. 

In  like  manner  by  drawing  in  the  crest  of  the  glacis- 
nearer  to  the  scarp  the  latter  will  be  better  masked  by  it 
from  the  plunge  of  the  distant  fire  of  the  assailant’s  bat- 
teries, and  cannot  be  breached  so  low  down  from  his  bat- 
teries placed  along  the  glacis  crest. 

On  the  other  hand,  when  the  ditch  is  too  narrow  it  may 
be  partly  filled  by  breaching  the  scarp,  and  then  blowing  ins 
the  counterscarp  so  as  by  the  united  dehris  to  form  an  easy 
roadway  for  an  assaulting  column  to  enter  the  work. 

A wide  ditch,  on  the  other  hand,  requires  more  labor  to* 
construct  the  trench  across  it  by  which  the  assailant  can 
reach  the  foot  of  the  breach  under  cover.  This  is  a con- 
sideration of  some  importance  in  wet  ditches,  where  the 


J5LEMEXTS  OE  PERMANENT  FORTIFICATION^'. 


11 


assailant  is  obliged  to  construct  a dike  upon  which  the  para- 
pet of  his  cover  is  placed. 

In  the  most  recently  constructed  forts  the  main  ditch  is 
limited  to  a depth  of  about  30  feet  and  a width  of  from 
13  to  16  yards.  Wet  ditches  have  a width  of  from  20  to  80 
yards  and  a denth  of  water  from  6 to  10  feet.  The  dimen- 
sions are  reduced  to  a minimum  where  the  embankments  are 
not  great  and  circumstances  are  unfavorable  to  an  attempt 
at  escalade. 

The  bottom  of  the  ditch,  when  dry,  usually  receives  a 
slight  slope  from  the  foot  of  the  scarp  and  counterscarp  to 
/its  centre,  where  a small  drain,  termed  a cunette,  is  dug  to 
receive  the  surface-water  and  keep  the  ditch  dry.  In  some 
cases,  from  motives  of  economy,  the  difference  of  level  be- 
tween the  cunette  and  the  foot  of  the  counterscarp  wall  is 
increased,  thus  giving  a less  height  of  wall.  This  practice, 
however,  can  only  be  followed  where  the  foundations  of  the 
wall  will  be  secure,  from  the  soil  of  the  bottom  of  the  ditch 
being  of  such  a nature  as  not  to  yield  from  the  effects  of  the 
weather  upon  it. 

13.  Face  Covers.  Engineers  since  the  times  of  Cor- 
montaigne  have  until  recently  adopted  his  method  of  placing 
the  top  of  the  scarp  wall  on  a level  with  the  crest  of  the 
glacis,  or  a little  below  this  crest,  to  give  the  wall  cover  from 
the  assailant’s  distant  batteries.  But  this  is  evidently  only  a 
partial  remedy,  since  the  plunge  of  projectiles  fired  from  a 
distance  is  very  great  in  the  descending  branch  of  the  tra- 
jectory, and  with  the  rifled  guns  now  used,  these  projectiles 
fired  from  a distance  may  pass  over  the  glacis  crest  and  strike 
the  wall  quite  low  down,  thus  effecting  serious  damage,  par- 
ticularly in  the  case  of  wide  and  shallow  ditches. 

Yarious  expedients  have  been  proposed  by  engineers  to 
remedy  this  defect.  Choumara,  an  engineer  of  celebrity, 
has  proposed  to  form  what  he  terms  an  interior  glacis  within 
the  ditch,  the  crest  of  which  shall  rise  so  high  above  the 
bottom  of  the  ditch,  that  it  shall  mask  the  scarp  wall  from 
the  plunge  of  the  distant  batteries,  and  shall  force  the 
assailant  to  establish  his  breaching  batteries  on  this  interior 
glacis  to  enable  him  to  fire  low  enough  to  effect  a practi- 
cable breach  in  the  wall. 

Brialmont,  a more  recent  waiter,  proposes  a like  plan  for 
the  same  purposes  ; and  in  one  of  our  own  works.  Fort 
Warren,  Boston  Harbor,  a heavy  earthen  face-cover  masks 
a portion  of  the  scarp  wall,  from  a position  from  which  a 


12 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


breaching  fire  might  have  been  brought  against  the  part 
thus  masked. 

The  latest  practice,  when  face-covers  are  not  used,  is  to 
give  the  crest  of  the  glacis  the  depth  and  width  of  the 
ditch,  and  the  height  of  the  scarp  wall  such  relations  that  at 
least  16  feet  of  the  scarp  wall  is  covered  bj  the  glacis  from 
a plunging  fire  of  J.  See  Plate  1,  Figs.  1,  2,  3,  4,  and  5. 

14.  General  Remarks.  The  command  of  the  parapet 
over  the  exterior  ground  and  any  outworks  of  the  defences, 
its  reliefs  or  height  above  the  bottom  of  the  ditch,  and  its 
height  above  the  top  of  the  scarp  wall,  are  all  points  which 
call  for  a careful  consideration  on  the  part  of  the  engineer 
in  any  combination  of  these  that  he  may  be  called  upon  to 
make. 

First,  it  is  important  that  the  parapet  should  thoroughly 
sweep  all  the  ground  within  range  of  its  guns,  at  least  up 
to  the  glacis  crest ; and  the  more  so  as  the  closer  the 
assailant’s  trenches  approach  the  work,  the  greater  will  be 
the  plunge  obtained  upon  them,  and  the  more  difficult  it 
will  be  for  the  assailant  to  cover  himself  by  his  trenches. 

That  the  parapet  should  command  all  outworks  within 
range  of  its  nre  is  obvious,  otherwise  when  seized  upon  by 
the  assailant  these  outworks  would  have  a plunging  fire 
upon  the  main  work. 

. The  rule  is  laid  down  by  some  authorities,  that  the  pro- 
jectiles of  the  parapet  should  clear  the  crest  of  the  glacis 
by  at  least  2 feet.  But  this  is  by  no  means  necessary,  for  if 
the  glacis  has  a covered-way  for  troops  in  its  rear,  it  will  be 
impracticable  to  keep  these  troops  in  the  covered-way 
with  missiles  passing  in  such  close  proximity  to  them,  par- 
ticularly as  the}"  are  subjected  to  danger  from  the  blast,  gas 
checks,  and  unburned  powder-grains,  as  well  as  from  the 
bursting  of  shells  in  their  rear. 

The  relief  of  the  parapet  of  the  ffanking  parts  of  the  work 
should  evidently  be  such  that  every  point  along  the  foot  of 
the  scarp  wall  shall  be  swept  by  its  fire.  This  supposes  also 
a certain  correlation  between  the  relief  and  the  length  of 
the  lines  flanked,  so  that  this  condition  shall  be  satisfied  ; a 
relation  that  can  always  be  easily  found,  either  by  calcula- 
tion, or  a very  simple  geometrical  construction  from  given 
data. 

In  like  manner  the  height  of  the  interior  crest  of  the 
parapet  above  the  top  of  the  scarp  wall  can  be  easily 
ascertained  by  the  same  methods,  with  assumed  data.  It 
should  evidently  be  at  least  such  that  a gun,  on  any  kind  of 


ELEMENTS  OF  PERMANENT  FORTIFICATION.  13« 

carriage,  firing  through  an  embrasure  of  assumed  depth  and 
under  a given  depression,  should  clear  the  coping  of  the  wall 
about  one  foot. 

A mere  geometrical  diagram  will  show  that  as  the  height 
of  the  interior  crest  above  the  top  of  the  w^all,  supposing  the 
position  of  the  latter  fixed,  is  increased,  the  whole  parapet 
will  be  thrown  further  back  from  the  wall,  and  the  interior 
space  of  the  work  will  be  in  the  same  degree  lessened. 

All  of  these  considerations  therefore  suggest  that  nothing 
like  absolute  rules  can  be  laid  down  so  as  to  give  a routine 
character  to  the  practice  of  this  branch  of  the  military  art. 

The  rules  here  giv^en  with  respect  to  the  form  and  dimen- 
sions of  the  general  profile  of  the  enceinte  are  founded  upon 
reasons  growing  out  of  the  nature  of  tlie  question,  and  as 
such  have  served  as  guides  to  engineers  in  the  practice  of 
their  profession.  As  they  have  stood  besides  tlie  test  of 
long  experience,  it  is  safe  to  follow  them,  whilst  at  the  same 
time  the  engineer  should  not  hesitate  to  vary  from  them 
when  satisfied,  after  careful  examination,  that  the  case 
before  him  requires  it.  Fortification,  it  must  be  remem- 
bered, is  like  all  other  arts : it  has  its  canons,  which  are 
founded  upon  the  nature  of  the  question,  and  its  rules  of 
practice  based  upon  these  and  upon  experience.  As  the 
latter  presents  to  the  engineer  new  facts,  his  practice  must 
be  made  to  conform  to  them ; but  the  general  principles  of 
his  art  must  ever  remain  the  same,  and  be  his  invariable 
guide. 


III. 

OPEN  DEFENCES. 

15.  By  this  term  are  understood  the  dispositions  made 
for  the  action  of  the  troops  and  armament  which  afiord 
cover  only  from  the  direct  fire  of  the  assailant. 

To  this  class  belong  the  arrangement  of  the  parapet 
which  has  already  been  described  ; simple  loop-holed  walls 
for  musketry  used  as  inclosures  of  gorges,  detached  scarps, 
etc. ; exterior  corridors  which  are  covered  either  by  a wall 
or  an  earthen  parapet ; and  harhettes  and  embrasures  for 
artillery. 

16.  Loop-Holed  Walls.  Walls  of  this  class,  when 
used  as  the  inclosures  of  the  gorges  of  lunettes  or  other 
isolated  works,  placed  in  advance  of  the  enceinte,  but  within 


14 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


the  reach  of  its  artillery  fire,  should  be  high  enough  to 
secure  the  work  from  an  open  assault,  and  sufficiently  thick 
to  resist  the  occasional  shot  which  may  reach  them  over  the 
parapet  by  which  they  are  covered.  For  these  purposes 
the  height,  Plate  4,  Fig.  24,  should  be  from  12  to  15  feet, 
and  the  thickness  from  4 to  5 feet.  The  loop-holes  are  not 
placed  nearer  to  each  other  than  from  3 to  4 feet,  estimated 
between  their  axes.  They  shoidd  be  at  least  6 feet  above 
the  exterior  foot  of  the  wall,  and  4^  feet  above  the  ground 
or  banquette  within.  The  loop-holes  are  usually  placed  at 
regular  intervals  along  the  line  of  the  wall,  or  only  opposite 
that  portion  of  the  exterior  ground  upon  which  a fire  is  to 
be  brought  to  bear. 

The  form  and  dimensions  of  the  loop-hole  will  depend 
upon  the  thickness  of  the  wall  and  the  field  of  view,  both 
vertically  and  horizontally,  which  is  to  be  covered  by  its  fire. 
The  plan  is  either  trapezoidal,  Plate  4,  Figs.  IT,  20,  widen- 
ing from  the  front  of  the  wall  inwards,  or  else  it  widens 
from  the  centre  each  way  to  the  front  and  back ; or,  as  is 
the  more  usual  form  in  our  works,  the  interior  portion  from 
the  centre  widens  inwards,  whilst  the  exterior  part  is  rectan- 
gular in  plan,  and  of  the  same  width  as  the  width  on  the 
interior  or  back  of  the  wall.  The  first  form  is  best  adapted 
to  walls  not  more  than  2J  feet  thick,  the  others  to  heavier 
walls ; the  object  being  to  lessen,  as  far  as  practicable,  the 
weakness  which  loop-holes  necessarily  cause  to  the  wall ; this 
defect  increasing  as  the  exterior  or  interior  opening  is  greater. 

For  thin  walls,  where  the  plan  of  the  loop-hole  is  trape- 
zoidal, the  width  of  the  exterior  opening  may  be  from  2 to 
4 inches,  and  that  of  the  interior  from  15  to  18  inches. 
These  dimensions,  however,  may  vary  according  to  the  field 
of  fire  to  be  brought  within  the  range  of  the  loop-hole,  the 
more  or  less  cover  to  be  given  to  the  troops,  and  the 
strength  of  the  masonry  of  which  the  wall  is  formed.  The 
vertical  dimensions  of  the  loop-hole,  both  on  the  interior  and 
the  exterior,  will  depend  upon  the  field  of  fire  to  be  em- 
braced in  this  last  direction,  and  they  will  be  regulated 
accordingly ; the  top  and  sole  of  the  loop-hole  receiving  a 
suitable  slope  or  direction  for  this  purpose. 

The  foregoing  details  can  only  be  well  determined  upon 
from  the  special  object  to  which  the  loop-holed  defences  are 
to  be  applied.  Care  only  is  to  be  taken  that  in  attempting 
to  give  cover  to  the  troops  their  field  of  view  be  not  too 
restricted  by  too  narrow  an  opening  for  the  use  of  the  fire- 
arms. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


15 


Where  the  throat  or  narrowest  part  of  the  loop-hole  is 
■within  the  w'all,  the  exterior  opening  leaves  a wider  mark 
for  the  missiles  of  the  assailed,  and  when  the  sides  of  the 
loop-hole  gradually  widen  outw^ards,  a shot  striking  one  of 
them  may  glance  inward  and  do  injury. 

To  prevent  this  accident,  the  sides,  and  sometimes  the 
sole,  are  made  in  offsets.  A more  convenient  form  for  con- 
struction, and  one  better  adapted  for  arresting  the  enemy’s 
balls,  is  to  make  the  exterior  portion  rectangular  in  plan 
for  half  the  width  of  the  wall  as  already  described. 

The  best  form  is  a modification  of  this  made  by  placing 
at  the  throat  a plate  of  iron  or  steel  pierced  by  an  opening 
generally  2 by  5 inches. 

17.  Exterior  Corridors.  In  open  exterior  corridors 
the  troops  are  covered  in  front  either  by  an  earthen  parapet, 
which  is  usually  only  musket-proof,  the  scarp  wall  being  run 
up  to  the  superior  slope  ; or  else  the  scarp  wall  serves  as  the 
cover,  in  which  case  it  is  pierced  either  throughout  its 
length  or  at  suitable  points  with  loop-holes.  The  floor  of 
the  corridor,  c,  Plate  4,  Fig.  27,  serves  as  a banquette  tread 
for  the  loop-holes,  and  is  therefore  placed  with  reference  to 
the  direction  < ^ the  fire  from  the  loop  holes.  The  height  to 
which  the  scarp  w^all  rises  above  the  floor  of  the  corridor 
will  depend  upon  the  level  of  the  floor,  and  that  of  the  bot- 
tom of  the  ditch ; this  heiglit,  however,  should  not  be  less 
than  G^-  feet  to  afford  a sul&ient  cover  to  the  troops. 

The  preceding  Fig.  27  is  given  as  an  example  of  a semi- 
detached scarp,  A,  an  earthen  counterscarp  and  covered-wTiy, 
D ; being  a section  of  an  outwork  of  one  of  our  sea-coast 
forts. 

18.  Barbette  Batteries.  For  guns  mounted  on  the 
ordinary  field  and  siege  carriages,  the  barbettes  are  con- 
structed in  the  same  manner  and  with  the  same  dimensions 
as  in  field-works;  the  arrangement  of  the  ramps  and  the 
slopes  being  determined  by  the  position  in  which  the  bar- 
bette is  placed,  and  its  relative  position  with  respect  to  the 
terre-plein  and  parapet. 

For  the  heavy  guns  used,  both  for  land  and  sea  fronts,  a 
solid  foundation  of  concrete  and  stone,  with  the  necessary 
iron  work,  is  laid  to  receive  the  gun  with  its  carriage,  and 
to  allow  it  to  be  worked  efficiently.  To  protect  the  guns 
against  flank  fire,  large  traverses  (generally  containing  bomb- 
proof constructions)  are  used.  These  traverses  are  extended 
upon  the  parapet  so  as  to  form  bonnets^  affording  the  greatest 
cover  consistent  with  a wdde  field  of  fire. 


16 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


Carriages  have  been  designed  which  allow  the  gun  to  be 
lowered  behind  the  parapet  for  loading,  and  raised  above  it 
for  firing  (see  Plate  7). 

The  modifications  of  parapet,  already  referred  to,  to  suit 
special  carriages  and  guns,  are  very  marked  when  this  class 
of  carriage  is  used,  also  when  arrangements  are  made  for 
loading  the  guns  under  cover.  This  cover  is  obtained  by  v. 
making  bomb-proof  communications  and  chambers,  opening 
toward  the  gun,  under  the  parapet  and  traverses,  in  which 
the  machinery  for  loading  the  guns  is  placed,  and  which 
allow  the  ammunition  to  be  safely  carried  from  the  maga- 
zines to  the  guns. 

These,  or  similar  protections,  have  become  absolutely 
necessary  to  prevent  barbetfe  guns  being  silenced,  if  they 
are  exposed  to  the  close  fire  of  small-arms  and  machine 
guns. 

Where  ample  space  exists  for  placing  batteries  of  heavy 
guns,  with  considerable  command,  and  a favorable  soil,  par- 
ticularly for  coast  defence,  the  modification  of  parapet  may 
extend  even  to  sinking  a pit  for  each  gun  and  constructing 
bomb-proof  underground  communications,  magazines,  quar- 
ters, store-rooms,  etc.,  for  their  service. 

19.  Embrasure  Batteries.  The  embrasures  cut  in 
the  parapets  for  guns  on  field  and  siege  carriages  differ  in 
no  essential  point  from  those  for  field-works.  It  is  well, 
however,  to  observe,  as  the  parapet  is  weakened  by  receiving 
embrasures,  the  splay  given  to  them  should,  in  all  cases,  be 
carefully  regulated  by  the  field  of  fire  it  is  desirable  to  com- 
mand, so  as  to  leave  as  large  a mass  of  merlon  between  them 
as  practicable,  to  resist  the  assailant’s  fire. 

20.  Machicoulis.  For  the  purpose  of  attaining,  by 
musketry,  the  foot  of  a scarp  wall  without  flank  defences,  , 
resort  must  be  had  to  a machicoulated  arrangement  at  the 
top  of  the  scarp. 

The  usual  mode  adopted  for  this  purpose,  PI.  8,  Figs.  67, 
68,  is  to  form  a parapet  wall  which  rests  upon  a solid  hori- 
zontal band  of  stone,  near  the  top  of  the  scarp,  which  is 
supported  on  corbels  or  projecting  blocks,  firmly  built  into 
the  wall.  The  back  of  the  parapet  wall  is  placed  a few 
inches  in  advance  of  the  scarp,  leaving  room  for  the  slanting 
loop-holes  pierced  in  the  horizontal  band  through  which  the 
fire  is  to  be  delivered  on  the  foot  of  the  scarp.  The  top  of 
the  parapet  wall  is  also  arranged  to  admit  of  firing  on  more 
distant  points. 

In  the  example  given,  which  is  from  an  Austrian  author- 


ELEMENTS  OF  PEEMANENT  FORTIFICATION. 


17 


ity,  Fi^.  67  is  a front  elevation,  and  Fig.  68  a section  through 
a loop-liole. 

Figs.  65,  66  are  a front  elevation  and  section  through  a 
loop-hole,  from  the  same  authority.  This  is  a semi-detached 
scarp  wall,  the  top  portion  of  which  is  arranged  on  the  back 
with  loop-hole  recesses;  the  lower  portion  having  very  in- 
clined arched  recesses  in  front,  with  slanting  loop-holes  to 
tire  on  the  foot  of  the  scarp  from  the  upper  recesses. 

AVliere  from  the  irregularity  of  the  site  the  ordinary 
machicoulis  cannot  be  made  efficient,  resort  may  be  had  to 
small  polygonal  chambers  of  stone,  open  at  top,  and  having 
the  sides  and  bottom  pierced  with  loop-holes  and  machicoulis. 
These  constructions  may  be  made  just  of  sufficient  size  to 
hold  a single  sentinel.  They  are  placed  at  the  angles  of 
the  works  where  they  will  not  be  exposed  to  artillery,  and 
are  supported  on  a corbel  work  projecting  from  the  top  of 
the  scarp  wall. 

These  devices  will  be  rarely  if  ever  used  in  works  con- 
structed in  the  future,  since  they  are  absolutely  useless  if 
exposed  to  artillery  lire,  and  can  generally  be  replaced  by 
cheaper  and  simpler  constructions,  which  are  equally  efficient 
upon  fronts  not  so  exposed. 


lY. 

COVERED  DEFENCES. 

21.  Detached  Scarp  Walls.  When  the  scarp  walls 
are  entirely  detached,  leaving  an  open  corridor  between 
them  and  the  rampart,  they  are  pierced  with  one  or  two 
tiers  of  loop-holes,  from  which  a fire  can  be  brought  upon 
the  ditch  and  in  some  cases  upon  the  terre-plein  of  the 
covered-way.  or  any  work  in  front  of  the  enceinte. 

To  give  cover  to  the  men  at  the  loop-holes  arched  re- 
cesses, FI.  4,  Figs.  25,  26,  are  made  in  the  thickness  of  wall, 
or  else  short  counterforts  are  built  back  from  the  wall, 
which  serve  as  the  piers  of  covering  arches.  The  width  of 
the  recesses  should  admit  of  three  or  four  loop-holes  at  the 
usual  distance  apart,  their  height  and  depth  being  sufficient 
to  give  the  men  shelter  from  vertical  fire  and  allow  them 
to  handle  their  arms  with  convenience. 

The  two  Figs,  above  are  sections  of  this  description  of 
scarp  wall  taken  through  the  crowns  of  the  arches,  as  shown 
in  an  Austrian  work,  a is  a section  of  the  wall ; b and  d, 


18 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


elevations  of  the  sides  of  the  recesses;  c,  an  elevation  and 
section  of  the  recess  arch. 

22.  Semi-detached  Walls,  Fig.  28,  are  also  in  some 
cases  built  with  recesses.  Besides  these,  traverse  walls,  h,  are 
built  back  from  the  scarp  wall  into  the  parapet,  at  intervals, 
to  afford  cover  to  troops,  circulating  in  the  corridor,  from 
enfilading  fire,  and  to  admit  of  a defence  of  the  corridor  if 
the  assailant  should  enter  it  between  any  two  of  these  tra- 
verses. For  this  purpose  they  are  pierced  with  loop-holes, 
and  have  door-ways  for  circulation  throughout  the  corridor. 

23.  Scarp  Galleries.  In  the  permanent  works  of  more 
recent  construction  in  our  own  country  and  in  Europe 
revetment  w’alls  with  relieving  arches,  PI.  4,  Fig.  15,  have 
in  most  cases  been  introduced  instead  of  the  ordinary  thick 
walls  with  counterforts,  which  had  been  hitherto  the  usual 
mode  of  retaining  the  earth  of  the  rampart  and  parapet. 

The  piers  of  the  relieving  arches,  which  also  serve  as 
counterforts  to  the  revetment-wall,  are  rectangular  in  plan, 
and  usually  run  back  from  12  to  16  feet.  They  are  from  4 
to  6 feet  thick,  and  placed  from  12  to  18  feet  apart  be- 
tween their  centre  lines.  The  arclies  are  usually  full  centre 
and  2 feet  thick,  with  a rough  shaped  capping  which  adds 
an  additional  thickness  from  9 to  12  inches  over  the  crown 
of  the  arch. 

The  preceding  Fig.  is  a section  of  a revetment  wall  of 
this  kind,  of  one  of  our  forts,  through  the  curtain  in  front 
of  which  is  a mask  of  which  d is  the  section,  b is  an  eleva- 
tion of  the  face  of  the  pier;  c,  the  relieving  arch;  and  a, 
the  scarp  wall. 

This  mode  of  construction  offers  the  advantages  of  a more 
stable  structure  and  rendering  it  more  difficult  for  the  as- 
sailant to  make  a practicable  breach  in  the  wall,  whilst  by  a 
suitable  arrangement  of  the  relieving  arches  and  their  piers 
with  the  earth  of  the  rampart,  a sufficient  space  can  be 
secured  behind  the  scarp  wall  to  form  a gallery  for  defensive 
purposes. 

The  arches  and  piers  form  the  top  and  sides  of  the  gal- 
lery, the  scarp  wall  foi’ming  the  front,  and  the  back  or  rear 
being  either  ])artly  or  wholly  closed  by  a wall  which  retains 
tlie  earth  behind  it.  The  gallery  is  thus  divided  up  into 
chambers,  the  communication  between  which  is  effected  by 
doorways  made  through  the  piers. 

The  width  and  height  of  the  gallery  should  in  all  cases 
be  sufficient  to  allow  the  men  ample  room  for  handling 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


19 


their  fire-arms,  and  to  admit  of  a circulation  through  the 
gallery  when  the  troops  for  the  defence  are  posted  in  it. 

From  three  to  four  loop-holes  are  made  in  the  portion  of 
the  scarp  wall  that  forms  the  front  of  each  chamber.  The 
dimensions  and  forms  of  the  loop-holes  are  the  same  as 
already  described,  and  they  are  otherwise  arranged  for  de- 
fence as  in  detached  scarp  walls. 

In  PI.  4:,  Fig.  16,  a section  of  a scarp  gallery  constructed 
in  one  of  our  older  forts  is  shown,  a is  the  scarp  wall ; b 
the  pier  of  the  relieving  arch  c ; d the  rear  wall  which  closes 
the  gallery  and  sustains  the  earth  behind  it.  The  section 
also  shows  the  parts  of  the  rampart  and  parapet  and  the 
breast-high  wall  e. 

In  Figs.  IT,  18,  19,  the  plan,  section,  and  rear  elevation 
of  a gallery  are  shown  as  given  in  French  authorities.  The 
peculiarity  of  this  example.  Fig.  19,  consists  in  the  arrange- 
ment of  the  rear  of  the  gallery,  which,  instead  of  being 
entirely  closed  by  a wall,  is  only  partly  so  ; a small  wall,  a, 
which  rests  upon  an  arch,  b,  built  between  the  two  piers,  is 
placed  parallel  to  the  back  of  the  scarp  wall  and  at  a distance 
from  it  equal  to  the  width  of  the  gallery,  the  top  of  the  wall 
being  raised  to  the  level  of  the  surface  of  the  earthen  slope 
which  falls  in  behind  from  the  top  of  the  arch.  The  sec- 
tion, Fig.  18,  through  r s,  and  elevation.  Fig.  19,  show  the 
position  of  the  loop-holes,  and  the  vent  for  the  escape  of  the 
smoke  is  pierced  in  the  scarp  wall  just  below  the  crown  of 
the  arch,  b,  are  the  piers  ; a the  arches  with  their  capping  ; 
,D  the  doorways  through  the  piers. 

Figs.  20,  21,  represent  the  plan  and  section  of  a scarp 
gallery  in  two  tiers,  as  given  in  an  Austrian  work.  The 
rear  of  the  gallery  is  closed  by  a simple  wall.  Besides  the 
vent  holes  for  the  escape  of  smoke,  drains  are  made  in  the 
scarp  wall  at  the  level  of  the  gallery  floor  to  convey  off  any 
water  that  may  collect  in  it. 

Figs.  22,  23,  are  a plan  and  section,  from  the  same  author- 
ity, of  a gallery  behind  the  lower  portion  of  the  scarp  wall, 
the  upper  portion  being  connected  with  relieving  arches 
so  arranged  that,  being  open  to  the  rear,  the  foot  of  the 
slope  of  earth  will  just  touch  the  back  of  the  wall  at  its  foot 
within.  In  this  example  the  pressure  of  the  earth  being 
supposed  to  be  great,  the  gallery  is  closed  in  the  rear  by 
arched  walls  ; the  arches  being  built  into  the  vertical  piers 
B,  of  the  relieving  arches  c.  This  example  also  shows  the 
manner  of  barricading  the  doorways  through  the  piers  by 


20 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


vertical  grooves,  made  in  tlie  opposite  faces  of  the  piers,  to 
receive  the  scantling  forming  the  barricade. 

In  Fig.  28  is  shown  the  section  of  a gallery  behind  the- 
lower  portion  of  the  scarp,  with  tlie  upper  portion  arranged 
witli  recesses  for  loop-holes. 

These  same  methods  of  construction  are  now  adopted, 
with  changes  in  dimensions  resulting  from  the  different 
height  of  scarp  walls  and  the  need  of  an  additional  depth  of 
protection  against  vertical  lire. 

The  galleries  are  now  made,  almost  exclusively,  one  tier 
in  height,  the  arches  receive  a thickness  of  3 feet  of  brick 
or  concrete  and  a capping  of  12  to  18  inches  covered  with 
from  5 to  15  feet  of  earth,  according  to  their  exposure. 

24.  Counterscarp  Galleries.  PI.  1,  Fig.  35.  The 
most  simple  method  of  arranging  a gallery  behind  a coun- 
terscarp wall  for  the  defence  of  a ditch  is  to  build  another 
wall  parallel  to  that  of  the  counterscarp,  and  to  throw  an 
arch  over  between  the  two  to  cover  the  top  of  the  gallery. 
The  counterscarp  wall  is  pierced  with  loop-holes  arranged  in 
the  same  way  as  in  scarp  galleiles. 

The  example  selected  is  from  one  of  our  works,  and 
shows  a section  of  the  gallery  through  a loop-hole,  a,  coun- 
terscarp wall ; D,  parallel  wall ; c,  arch  and  capping  ; e,  gla- 
cis mask  covering  the  scarp  wall. 

In  Figs.  29,  30,  31,  are  shown  a plan,  section  on  r s,  and 
a section  and  interior  elevation  on  o of  a counterscarp 
gallery  taken  from  a French  authority.  In  this  case  coun- 
terforts, square  in  plan,  are  built  along  the  back  of  the 
counterscarp  wall,  leaving  8 feet  between  them.  Parallel 
to  the  counterscarp  wall  and  4 feet  in  rear  of  the  coun- 
terforts another  wall  is  built,  which,  with  the  counterforts, 
serves  as  the  support  of  a series  of  arches  perpendicular  to 
the  counterscarp  wall  sprung  between  the  counterforts,  and 
another  parallel  to  it  and  resting  on  the  counterforts  and  par- 
allel wall.  The  arches  between  the  counterforts  form  with 
them  recesses,  a,  for  the  men  serving  the  loop-holes  pierced 
in  the  counterscarp  wall ; whilst  the  covered  space,  b,  in  rear 
serves  for  circulation  without  disturbing  the  men  engaged 
in  tiring. 

Counterscarp  galleries  may  also  be  arranged  for  a ditch 
defence  with  artillery ; howitzers,  rapid-firing  and  machine 
guns  are  used  for  this  purpose.  A plan,  Fig.  32,  a vertical 
section  and  side  elevation  on  d c,  Fig.  33 ; and  a section  and 
back  elevation  on  a b.  Fig.  34,  taken  from  one  of  our  works, 
show  a disposition  of  this  kind  in  the  reentering  angle  of 
the  counterscarp. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


21 


25.  Bastionnets.  In  small  works,  where  a flanking 
disposition  cannot  be  obtained  from  the  enceinte,  as  in  lu- 
nettes and  redoubts,  the  ditches  may  be  swept  by  covered 
chambers,  PI.  5,  Fig.  39,  attached  to  the  scarp  wall  either 
at  the  centre  of  the  sides  of  the  work,  or  at  the  angles. 

These  chambers,  PL  5,  Fig.  39,  are  usually  of  a pentago- 
nal form,  the  sides  wPich  join  the  scarp  wall  serving  to 
flank  it,  and  the  two  exterior  sides,  forming  a salient  angle, 
delivering  their  Are  on  the  opposite  counterscarp  and  its 
crest.  From  their  form  and  purposes  they  have  received 
the  name  of  bastionnets. 

The  dimensions  of  these  constructions  wdll  depend  upon 
the  amount  and  kind  of  fire  to  be  delivered.  Their  scarps 
should  be  as  high  as  that  of  the  main  work.  The  entrance 
to  them  is  either  directly  from  a parade  by  a postern,  or 
from  a scar])  gallery  which  flanks  them. 

Fig.  39  shows  a plan  of  bastionnet,  d,  at  an  angle  com- 
municating with  a scarp  gallery,  e.  In  rear  of  the  scarp 
gallery  and  opposite  to  the  bastionnet,  is  placed  a small 
powder-magazine  for  its  service.  The  example  is  from  an 
Austrian  authority,  and  is  arranged  for  one  small  gun  on 
each  flank,  besides  the  loop-holes  for  small-arms. 

As  a general  rule,  it  may  be  laid  down  that  the  salient 
angles  of  the  redoubt  are  the  most  suitable  positions  for 
the  bastionnets.  as  they  will  thus  form  small  bastioned 
fronts,  in  which  both  the  faces  of  the  main  work  and  those 
of  the  bastionnets  will  be  swept  by  the  flanks  of  the  latter. 
The  only  danger  in  this  arrangement  is  that  the  loop-holes 
in  one  flank  may  be  tired  into  from  the  opposite  one.  This, 
however,  may  be  guarded  against  by  a suitable  position 
given  to  the  loop-holes. 

As  the  main  object  of  covered  defences  is  protection 
against  shells,  it  is  essential  that  the  arches  of  the  galleries 
and  bastionnets  should  be  bomb-proof.  The  thickness  pre- 
viously given  is  generally  thought  necessary,  but  where  the 
span  of  the  arch  is  very  small  the  thickness  of  the  brick 
may  be  reduced  to  2 feet. 

With  regard  to  the  front  walls  of  these  constructions,  as 
they  are  too  vveak  to  withstand  the  direct  action  of  artillery, 
they  must  either  be  covered  by  earthen  masks,  as  a glacis 
raised  beyond  the  counterscarp  for  example,  or  be  used  only 
in  positions  where  they  are  not  exposed  to  this  fire. 

General  Remarks.  It  should  be  observed  that  wdiat- 
ever  advantages  covered  defences  afford  as  shelter  from  the 
assailant’s  fire,  they  present  the  inconveniences  of  a com- 


2:1  ELEMENTS  OE  PERMAXEXT  FORTIFICATION. 

parativelj  narrow  and  obstructed  field  of  view  to  the  as- 
sailed, which  is  further  obscured  bj  the  smoke  which  may 
gather  within  the  gallery,  and  in  front  of  the  loop-holes. 
From  these  causes  the  assailed  having  to  aim  at  a venture, 
his  fire  is  likely  to  be  less  effective  than  in  open  defences, 
where  the  smoke  disperses  rapidly  and  leaves  a clear  field 
of  view.  The  same  may  be  said  of  loop-holed  walls  cover- 
ing exterior  corridors  where  the  space  to  the  rear  is  confined. 

Owing  to  these  considerations,  loop-hooled  and  covered 
defences  of  the  kind  in  cpiestion  should  be  restricted  to 
special  defensive  purposes,  where  an  object  within  the  field 
of  fire  can  be  attained  with  some  certainty  whether  seen  or 
not  by  the  assailed ; as,  for  example,  the  protection  of  a 
ditch,  or  a scarp  wall  which  cannot  be  flanked  from  within 
the  work ; for  sweeping  a covered-way,  or  the  interior  of 
any  outwork  which  cannot  be  brought  well  under  the  fire 
of  the  parapet  of  the  main  work. 

26.  Caponniere  Defences  for  the  Enceinte  Ditch. 
These  works  are  classed  under  the  head  of  what  are  termed 
defensive  casemates,,  which  are  bomb-proof  arched  structures 
for  receiving  cannon,  firing  through  embrasures  pierced  in 
the  front  or  mask  wall  of  the  casemates.  Defences  of  this 
class,  when  used  to  flank  the  ditch,  are  usually  termed  case- 
mated  caponnieres. 

These  defences  are  usually  placed  in  the  ditch  at  the 
middle  point  of  the  side  or  front  to  be  flanked.  The  out- 
line of  their  plan  is  mostly  that  of  a lunette,  PI.  5,  Fig.  36, 
the  flanks  being  perpendicular  to  the  line  of  the  scarp,  and 
the  two  faces  making  a salient  angle  of  60°.  The  capon- 
niere is  either  built  in  juxtaposition  with  the  enceinte,  or 
else  detached  from  it.  In  the  latter  case  an  inclosure  is 
formed  between  the  two  by  a loop-holed  wall  which  con- 
nects the  flanks  with  the  scarp  wall.  Each  flank  consists  of 
one  or  two  tiers  of  arched  chambers,  the  piers  of  the  arches 
being  perpendicular  to  the  back  of  the  walls  of  the  flank. 
Each  chamber  is  of  sufficient  dimensions  for  the  service  of 
a single  gun  with  a contracted  field  of  fire.  (PI.  5,  Figs. 
36,  37.)  In  some  cases  loop-holes  are  pierced  for  small- 
arms  on  each  side  of  the  embrasure  ; in  others  the  casemates 
of  one  story  are  pierced  for  cannon,  and  the  other  for  small- 
arms. 

The  casemates  are  closed  in  rear  by  a thin  wall,  which  is 
provided  with  windows  for  light  and  ventilation ; and  the 
])iei*s  are  pierced  with  doorways  to  form  a communication 
between  the  chambers  and  to  assist  the  ventilation.  Flues 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


23 


or  vents,  Fig.  37,  are  made  in  the  front  wall,  just  under  the 
arcdies,  for  a like  purpose.  Where  it  may  be  necessary,  the 
lower  floor  is  drained  by  a conduit  through  the  front  wall. 

An  open  court  is  left  between  the  flanks,  and  each  flank 
is  covered  at  top  with  from  6 to  12  feet  of  earth.  The 
flanks  are  separated  from  the  faces  by  a closed  corridor 
which  serves  as  a communication. 

In  front  of  the  corridor  and  on  each  side  of  the  axis  of 
the  caponniere  on  second  floor,  a casemated  chamber,  which 
is  open  in  front,  is  arranged  for  one  mortar.  Figs.  36.  38. 
The  arches  of  these  chambers  rise  towards  the  front  the 
better  to  subserve  the  object  in  view. 

On  one  side  of  the  chambers  on  first  floor  the  powder 
magazine  is  placed,  with  a store-room.  On  the  other  side 
a stairway  between  the  stories  is  built. 

The  space  within  the  salient  angle,  inclosed  by  the  walls 
of  the  faces  and  the  front  of  the  mortar  casemates,  is  open 
at  top.  It  has  an  open  corridor  on  the  second  story  for 
communication,  and  the  front  walls  are  arranged  with  loop- 
holed  recesses  for  small-arms.  Figs.  36,  38. 

The  enceinte,  in  the  rear  of  the  flanks  of  the  caponniere, 
is  arranged  with  a scarp  gallery,  to  flank  the  caponniere 
flanks  and  the  court  between  them.  A break  is  in  some 
cases  made  in  the  line  of  the  scarp  wall,  perpendicular  to 
the  caponniere  faces,  and  casements  for  cannon  and  small- 
arms  arranged  behind  the  scarp  wall,  to  flank  these  faces. 
In  some  cases  these  flanking  dispositions  are  placed  in  front 
of  the  scarp  wall,  the  casements  being  open  to  the  rear,  look- 
ing on  a narrow  court  between  them  and  the  scarp  which 
is  closed  on  the  sides  by  a loop-holed  w^all. 

The  example  here  given  of  a casemated  caponniere  is 
from  an  Austrian  authority.  Fig.  36  is  the  plan  ; Fig.  37, 
a section  and  elevation  on  ab  of  one  flank,  and  the  end  wall 
of  the  corridor  looking  tow^ards  the  court  between  the 
flanks ; Fig.  38,  a section  and  elevation  along  & d'  of  the 
corridor,  mortar  casemate,  and  triangular  court.  Figs.  37, 
38,  are  on  an  enlarged  scale. 

This  construction,  if  subject  to  artillery  fire,  as  it  will  be 
in  the  close  attack,  is  readily  destroyed.  It  is  valuable  ordy 
to  resist  escalade  or  assault  in  the  early  stages  of  the  attack. 

To  preserve  it  in  condition  to  be  effective  for  the  last 
stages  of  the  defence  has  been  the  study  of  the  advocates  of 
the  polygonal  system. 

The  latest  forms  differ  from  that  described  in  having  but 
one  tier  of  casemates,  covered  with  earth  which  may  be 


24 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


arranged  as  a parapet,  or  simply  as  a protection  to  the 
arclies.  The  face  wall  of  the  casemates  is  protected  from 
fire  by  being  set  back  so  far  from  the  heads  of  the  arches, 
that  a shot  coming  from  the  crest  of  the  glacis  and  pass- 
ing just  under  the  crown  of  the  arch  will  strike  the  ground 
below  the  embrasure.  (Plate  1,  Pig.  7.) 

This  requires,  when  the  exterior  side  is  great,  an  arch  of 
considerable  length,  which  by  retaining  the  smoke  of  dis- 
charge obstructs  the  view,  and  interferes  with  the  ventila- 
lation  of  the  caponniere. 

This  difficulty  is  alleviated  by  leaving  an  opening  between 
the  face  wall  and  the  tunnel-shaped  arches  for  the  escape  of 
smoke,  and  shielding  the  face  wall  by  giving  additional 
height  to  the  earth  cover  of  the  tunnel  arches.  (Plate  1, 

Fig.  8.) 


When  these  arches  are  subject  to  accurate  battering  tire  the 
(lehris  from  their  heads  will  obstruct  the  tire  of  the  capon- 
niere guns,  and  when  the  heads  are  battered  away  the  face 
wall  will  be  easily  breached  and  rendered  useless.  The 
advantage  of  the  new  over  the  old  form  consists  in  adding 
to  the  time  necessary  for  the  reduction  of  the  work. 

For  important  works  which  justify  the  expense,  armored 
caponnieres,  either  stationary  or  revolving  turrets,  are  pro- 
posed. Their  faces  may  be  of  sufficient  strength  to  with- 
stand the  besieger’s  guns,  or  they  may  be  raised  to  work 
their  guns  and  lowered  in  a pit  to  shield  them  from  fire. 
Their  tops  can  only  be  struck  obliquely  in  either  case. 
They  will  be  more  fully  described  hereafter.  \ 

27.  Casemates  on  Land  Fronts.  V arious  modes 
ave,  from  time  to  time,  been  proposed  for  arranging  de- 
fensive casemates  for  the  exterior  defence  ( f land  fronts. 
The  difficulty  in  covering  the  masonry  from  the  batteries  of 
the  assailant  has  been  the  chief  objection  to  tliese  structures, 
and  is  the  more  prominent  as  the  lire  of  ar  ;illery  becomes 
more  accurate,  as  such  casemates  would  soor  be  ruined  or 
rendered  untenable  by  embrasure  shots. 

The  Haxo  casemate,  named  from  its  desigi  er,  Gen.  Haxo, 
has  been  extensively  used.  These  casemates  consist  (Plate 
6,  Figs.  45,  46,  47,  48,  and  49)’  of  a series  o I arched  bomb- 
proof chambers  closed  in  front  by  a thin  mi  ,sk  wall  which, 
except  around  the  embrasures  through  it,  i i covered  from 
the  assailant’s  artillery  by  the  parapet.  To  present  but  a 
small  surface  of  masonry  to  fire,  the  arcl  es,  which  are 
horizontal  and  perpendicular  to  the  mask  wall  for  the 
greater  portion  of  their  length,  descend  towards  the  front. 


ELEMENTS  OF  PERMANENT/ FOKTIFICATION* 


25 


leaving  where  they  join  the  mask  pall  just  sufficient  height 
within  for  the  service  of  the  gun.  j To  effect  this  the  ante- 
rior portion  of  the  arch  must  be  c|)noidal  in  shape. 

The  piers  of  the  arches  are  pierced  with  wide  arched 
openings  which  serve  the  double  purpose  of  a communica- 
tion between  the  casemates  and  io  give  the  gun  a wider 
traverse  for  firing.  j 

Embrasures  are  pierced  in  the  /parapet  in  prolongation  of 
those  of  the  mask  wall,  and  it  is  proposed  to  cover  the  small 
portion  of  the  masonry  necessarily  exposed  by  this  arrange- 
ment by  placing  several  thicknesses  of  heavy  timber  in  front 
of  it  to  receive  the  shot,  or  to  cAe  it  with  wrought-iron. 

When  the  casemates  serve  simply  for  the  cover  of  the 
cannon,  the  arches  are  covered  with  from  4 to  6 feet  thick- 
ness of  earth,  and  are  left  ope  n to  the  rear  for  the  more 
prompt  escape  of  the  smoke,  an  1 a ditch  is  sometimes  made 
just  in  rear  of  the  casemates  to  catch  bombs  and  limit  the 
effects  of  their  explosion.  ^Hien  the  arches  are  made 
longer  than  for  the  service  of  ithe  guns  alone,  the  earthen 
covering  is  sometimes  arrangell  with  a parapet  to  cover 
cannon  in  barbette,  or  for  smalllarms. 

The  example  shown  by  the  Fibs,  is  from  a French  author- 
ity. Fig.  45  is  a plan  on  m n,|Fig.  47 ; Fig.  46  a section 
and  interior  elevation  towards  the  mask  wall  on  o p,  Fig. 

elevation  on  r s.  Figs.  45, 


rrangement  of  two  case- 
Austrian  authority.  In 
n the  flanks  from  enfl- 
interior  elevation  of  the 


47 ; and  Fig.  47  a section  and  si 
46. 

In  Figs.  48,  49  is  shown  an 
mates  of  the  Haxo  kind  from  a 
this  case  the  masonry  is  covered 
lading  Are  by  earth.  Fig.  48  is  a 
arches,  and  the  back  wall  that  reta|ns  the  earth  on  the  sides. 
Fig.  49  is  a longitudinal  section,  atid  shows  the  manner  of 
covering  the  masonry  in  front  aad  securing  the  earthen 
embrasure  by  a timber  facing.  I 

The  attempt  to  remedy  the  defeats  of  the  Haxo  casemate 
by  strengthening  the  face  wall  wiili  iron  and  removing  the 
objectionable  embrasure  in  the  earthen  parapet  has  led  to 
the  development  of  the  iron  and  |teel  constructions  wdiich 
are  applied  to  sea-coast  works,  but  which  have  been  used 
more  sparingly  on  land  fronts  owi^g  to  their  great  expense 
and  the  difficulty  of  flnding  a metal  which, will  resist  long- 
continued  direct  battering.  The  latter  difficulty  may  be 
overcome  by  the  use  of  inclined  armor. 

28.  Mortar  Casemates.  Iri  Fig.  50,  PI.  6,  is  shown 
\a  longitudinal  section  of  a mortar  casemate  placed  in  rear 


2G 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


of  a parapet,  by  wliich  it  is  covered  from  direct  fire.  TliC' 
arch  is  covered,  as  in  the  preceding  case,  by  earth,  to  break 
the  shock  of  shells.  It  rises  towards  the  front  to  give 
ample  room  for  the  shell  in  its  flight.  The  casemates  are 
covered  on  their  flanks  from  enfilading  fire  by  an  embank- 
ment, and  are  partly  closed  by  a wall  in  the  rear.  A small 
ditch  is  made  in  front  of  the  chamber,  and  a slight  wall 
built  within  it,  to  give  cover  from  the  splinters  of  shells 
falling  between  the  parapet  and  the  casemate.  Arched 
chambers  are  in  some  cases  made  beneath  the  mortar  cham- 
bers which  serve  as  store-rooms  and  temporary  magazines. 

When  these  casemates  are  placed  in  rear  of  a portion  of' 
the  parapet  but  little  exposed  to  direct  fire,  the  thickness  of 
the  parapet  in  front  of  them  may  be  reduced,  and  the  in- 
terior slope  be  replaced  by  a breast-high  wall  along  the 
front  of  the  casemates,  in  order  to  give  better  cover  in  flank 
and  from  slant  fire,  by  throwing  forward  the  casemates  more 
under  cover  of  the  parapet. 

The  example  given  is  from  the  same  authority  as  in  the 
preceding  example  of  casemated  caponnieres. 

On  faces  exposed  to  plunging  fire  this  casemate  must  be 
lowered  so  that  its  arch  is  protected  by  the  parapet  from 
projectiles  passing  over  it. 

29.  Casemates  for  Water  Fronts.  In  the  casemated 
batteries  for  sea-coast  and  harbor  defences,  the  scarp  or  mask 
walls  of  the  chambers  for  the  guns,  being  exposed  to  the 
fire  of  ships  alone,  are  not  subject  to  the  accurate  breaching 
fire  which  land  fronts  may  be  called  upon  to  sustain. 
Masonry  walls  could  be  built  strong  enough  to  resist  single 
shots  from  the  ships’  guns  in  use  prior  to  about  1865-70. 
Under  these  conditions  were  built  our  existing  casemated 
masonry  forts,  whose  details  are  shown  in  Plates  5 and  6, 
Figs.  40  to  44,  inclusive. 

With  the  increase  in  the  power  of  ships’  guns  these  walls 
are  easily  penetrated,  and  they  are  no  longer  effective  as  a 
defence.  No  modifications  of  these  works  have  been  made 
in  this  country ; but  in  some  English  and  Continental  forts 
the  masonry  fronts  of  the  gun  chambers  only  have  been 
replaced  by  iron  shields,  leaving  the  rest  of  tbe  scarp  wall  of 
masonry  (a  construction  of  doubtful  value),  and  in  others 
the  entire  scarp  wall  has  been  built  of  iron,  the  original 
masonry  of  the  interior  of  the  work  only  being  retained. 

In  tlie  newer  casemated  works,  which  are  made  with  one 
tier  of  artillery  fire,  the  parts  exposed  to  fire  are  of  iron  or 
steel,  the  thickness  of  which  is  determined  by  the  intensity 


ELEMENTS  OF  PERMA^fENT  FORTIFICATION.  2T 

RE  cl  greater  or  less  obliquity  of  the  blow  to  which  they  are 
liable  to  be  subjected. 

30.  Turrets.  The  field  of  fire  from  casemates  being 
limited,  and  the  exposure  to  hostile  fire  of  the  embrasures 
and  muzzles  of  the  guns  while  loading  objectionable,  re- 
volving turrets  have  been  adapted  to  fortifications  to  remedy 
these  defects. 

Turrets  are  particularly  valuable  for  sites  exposed  to  fire 
from  all  sides,  as  by  their  construction  they  occupy  little 
space,  give  protection  against  plunging  and  reverse  as  well 
as  front  fire.  They  command  a wide  field  of  fire,  are  in- 
commoded by  smoke  no  more  than  open  defences,  and  lend 
themselves  to  the  use  of  the  best  possible  appliances  for 
loading  and  working  their  guns.  For  fortifications,  their 
weight  (which  is  objectionable  on  ships)  is  an  advantage 
when  they  are  struck  by  heavy  projectiles.  The  principal  ob- 
jection to  them  is  the  great  cost  not  only  of  the  turret  itself^ 
but  of  the  machinery  for  working  it  and  of  the  substructure. 

They  have  been  made  in  the  form  of  a vertical  cylinder 
or  a truncated  cone  with  a fiat  top,  an  oblate  spheroid,  with 
the  embrasures  just  above  the  equatorial  circumference  and 
a spherical  segment  with  the  embrasures  pierced  horizon- 
tally through  the  dome-shaped  top. 

The  first  forms  have  the  advantage  of  an  easy  mechanical 
construction  with  either  rolled  or  forged  plates,  and  the  dis- 
advantage that  they  may  be  struck  in  a direction  nearly  or 
quite  normal  to  the  surface. 

The  spheroid  can  only  be  made  of  cast  metal. 

The  dome  can  be  made  of  wrought-iron,  steel,  or  com- 
pound plates. 

The  last  two  forms  can  only  be  struck  obliquely  by  direct 
fire.  More  detailed  descriptions  of  some  of  these  will  be 
given  farther  on. 

31.  Embrasures.  The  form,  dimensions,  and  construc- 
tion of  embrasures  in  mask  walls  present  a problem  which 
has  offered  to  engineers  no  little  difficulty  in  finding  a satis- 
factory solution  by  which  the  best  cover  could  be  given  to 
the  guns  and  men  by  exposing  the  least  surface  to  embrasure 
shots,  whilst  the  guns  should  receive  a suitable  traverse  to 
command  a wide  field  of  fire. 

The  most  perfect  type  of  masonry  embrasure  was  that 
used  in  the  latest  casemates  constructed  in  this  country  ; it 
was  designed  by  General  Totten,  of  the  U.  S.  Engineers, 
and  is  known  by  his  name.  It  is  shown  in  Plate  8,  Figs.  Gl, 
62,  63,  and  64. 


;28 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


In  iron  construction,  the  problem  is  more  simple,  and  has 
l)een  solved  in  several  ways,  all  having  in  view  the  greatest 
field  of  fire  with  the  smallest  opening.  This  object  is  best 
accomplished  by  pivoting  the  gun,  for  both  horizontal  and 
vertical  movement,  as  nearly  as  possible  at  the  centre  of 
the  embrasure. 

When  the  gun  is  allowed  to  recoil,  the  carriage  must  be  so 
constructed  as  to  allow  it  to  move  back  without  jamming  in 
the  embrasure.  Some  of  the  most  recently  devised  carriages 
hold  the  gun  in  position  and  prevent  recoil  by  suitable 
strong  recoil  bars  and  arcs,  and  secure  the  muzzle  in  the 
embrasure  either  with  a ring  and  trunnions  (Griison’s 
method),  or  by  a spherical  enlargement  on  the  gun  and 
corresponding  socket  in  the  embrasure  (Krupp). 

In  others  the  recoil  is  prevented  by  the  direct  resistance 
of  the  pintle  or  platform.  The  muzzle  of  the  gun  should 
project  in  all  cases  not  less  than  one  foot  beyond  the  em- 
brasure; frequently  it  projects  much  more. 

In  revolving  turrets  the  gun  needs  no  horizontal  traverse, 
and  can  be  worked  in  an  embrasure  of  the  Griison  pattern, 
whose  height  is  about  once  and  a half  the  diameter  of  the 
gun  at  the  embrasure,  and  whose  breadth  is  about  two  inches 
greater  than  this  diameter. 

The  guns  are  aimed  by  sights  on  the  chase,  by  sighting 
through  the  bore,  by  peep  holes  over  the  embrasure,  or  by 
sights  placed  on  top  of  the  turret  or  casemate.  All  the 
guns  of  a battery  are  sometimes  pointed  by  using  fixed 
horizontal  and  vertical  arcs  properly  graduated,  and  pointers 
attached  to  the  gun  ; the  sighting  being  done  by  the  use 
of  a sight-bar  or  telescope  mounted  on  a suitable  lookout, 
and  provided  with  an  arc  and  pointer,  whose  readings, 
properly  corrected  for  parallax  and  tabulated,  give  for  each 
gun  its  correct  pointing. 

32.  Bomb-proof  Buildings.  Caseniated  bomb-proof 
quarters  are  indispensable  to  the  safety  and  comfort  of  the 
garrison  during  siege,  or  any  prolonged  attack  for  the  an- 
noyance or  reduction  of  the  work  by  a bombardment.  In 
some  cases  advantage  is  taken  of  a scarp  wall,  on  a land 
front,  which  is  well  covered  by  a glacis  or  other  face  cover 
to  form  in  its  rear  quarters  of  this  character.  In  others 
they  are  made  under  the  terre-plein  and  traverses  where 
their  entrances  and  face-walls  are  not  exposed  to  fire ; and 
when  sufficient  room  cannot  be  obtained  in  these  places 
constructions  similar  to  traverses  may  be  built  to  cover  ad- 
ditional space.  The  arches  to  resist  splinters  only  may  be  3 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


29 


feet  tliiek,  covered  with  6 feet  of  earth.  If  subject  to  a fire 
of  ^‘torpedo  shells,”  Brialmont  recommends  a thickness 
of  arch  of  from  6 to  10  feet.  Whenever  the  plan  of  the 
work  admits  of  it,  quarters  of  this  kind  should  be  arranged 
for  defence,  by  being  pierced  with  loop-holes  and  even  with 
embrasures  for  cannon.  Defensive  casemated  quarters  and 
keeps  have  formed  a prominent  feature  in  the  German 
school  of  permanent  fortifications,  but  where  retained,  they 
will  be  modified  so  as  to  expose  no  masonry  to  artillery  fire, 
and  will  serve  only  as  quarters,  and  as  a last  defence  and 
refuge  for  the  garrison  when  the  work  is  stormed.  Some 
modern  forts  have  been  built  without  keeps.  A fulfilment 
of  the  conditions  requisite  to  a strong  defence,  however,  re- 
quires that  the  interior  of  the  work  be  swept  by  the  fire  from 
galleries  and  casemates  into  which  the  garrison  may  retire 
when  the  parapet  of  the  work  is  carried  either  by  surprise 
or  assault.  This  last  defence  may  drive  out  the  assailants 
and  preserve  the  work.  It  will  in  any  case  afford  the  garri- 
son an  opportunity  to  surrender  without  the  great  losses 
which  follow  a successful  assault  upon  an  open  work.  Be- 
sides, it  will  add  largely  to  the  morale  of  the  garrison,  and 
lead  them  to  hold  the  parapet  longer  than  they  would  with- 
out it. 

33.  Powder  Magazine.  Powder  magazines,  when 
practicable,  should  be  placed  below  the  surface  of  the 
ground,  and  should  never  be  exposed  to  the  dii-ect  fire  of 
the  enemy.  The  structures  for  this  purpose  are  built  with 
strong,  full  centre  bomb-proof  brick  arches,  supported  on 
heavy  stone  piers  which  form  the  outward  walls,  and  to 
which  interior  buttresses  are  sometimes  added.  The  cap- 
ping of  the  arches  is  covered  with  from  10  to  16  feet  of  sol- 
idly packed  earth.  The  interior  of  the  magazine,  the  floors, 
and  the  doors  and  windows  are  built  with  a view  to  security 
from  fire;  and  to  preserve  the  powder  from  dampness, 
by  a good  system  of  drainage  around  the  foundations,  and 
of  ventilation  by  means  of  air-holes  made  through  the  piers, 
and  panels  of  copper  pierced  with  small  holes  placed  in  the 
doors.  No  iron  or  steel  fastening  or  sheeting  is  allowed  in 
any  part  of  the  structure ; and  in  arranging  the  air-holes 
through  the  piers  they  receive  a broken  direction,  and  have 
a copper  mesh-work  placed  across  them,  to  prevent  any 
combustible  material,  or  rats  or  mice,  penetrating  to  the  in- 
terior of  the  magazine. 

In  large  works  the  magazines  are  isolated  as  far  as  practi- 
cable from  the  enceinte,  so  as  not  to  endanger  it  should  an 


30 


ELEMEXTS  OF  PERMAXEXT  FORTIFICATIOX. 


accidental  explosion  take  place.  The  magazine  is  enclosed 
bj  a strong  high  wall  for  security,  and  is  provided  with 
lightning-rods.  In  small  works  they  are  placed  in  the  posi- 
tion least  exposed  to  the  assailanc’s  fire,  and  given  the  great- 
est amount  of  cover  which  can  be  obtained. 


y. 

COMMUNICATIONS. 

34.  General  Remarks.  The  communications  form  a 
Nery  important  element  in  the  defence  of  permanent  works. 
The  size  and  disposition  of  the  communications  should  vary 
with  the  character  of  the  work  in  which  they  are  placed. 

In  small  works,  which  from  the  size  of  their  garrisons  are 
calculated  to  make  only  a strictly  passive  defence,  commu- 
nications of  just  sufficient  dimensions  for  the  passage  of  the 
troops  from  point  to  point  will  serve  every  purpose,  and  can 
be  more  easily  barricaded  and  otherwise  defended. 

But  for  large  works  having  full  garrisons,  the  communi- 
cations should  be  such  that  sorties  of  all  arms  and  in  large 
bodies  can  be  quickly  made.  With  communications  of  this 
character  a besieging  force  would  be  constrained  to  adopt 
extraordinary  measures  of  safety,  keeping  large  guards  in 
the  trenches  to  secure  them  from  such  sorties,  to  which  they 
would  be  continually  exposed. 

35.  All  communications,  to  serve  properly  their  ends, 
^should  fulfil  the  following  conditions: 

1.  They  should  uever^  from  their  ijosition^  comjyromise 
the  safety  of  the  enceinte. 

Frequent  instances  could  be  cited  of  works  which  have 
been  surprised  by  an  enemy  obtaining  possession  of  the 
gates.  Therefore  too  many  precautions  cannot  be  taken  to 
secure  the  principal  outlet  from  the  body  of  the  place  from 
.similar  attempts. 

2.  They  shoidd  admit  of  a convenient  circulation  of  the 
hesieged. 

To  subserve  this  purpose,  the  dimensions,  slopes,  etc.,  of 
the  posterns,  ramps,  and  other  similar  works,  should  be  con- 
venient for  the  service  to  which  they  are  applied,  and  they 
:should  be  placed  in  such  positions  as  lead  directly  to  the 
point  to  be  arrived  at. 

3.  llie  ^position  chosen  for  any  communication  should  he 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


31 


■moch  that  when  an  enemy  yets  possession  of  it^  he  may  ob- 
tain no  advantage  by  it. 

To  be  useless  to  an  enemy,  the  communication,  when  in 
liis  possession,  should  not  offer  a shelter  for  his  works  ; nor 
enable  him  to  carry  them  on  with  more  ease.  This  end  will 
be  obtained  by  placing  the  communications  in  a position  to 
be  enfiladed  by  the  fire  of  the  works  in  their  rear,  and  so 
arranging  them  as  to  preserve  the  counterscarp  wall  un- 
broken. 

4.  The  communications  shoidd  be  covered  from,  every 
point  where  an  enemy  might  establish  himself  dmdng  the 
whole  period  that  they  can  be  of  service  to  the  besieged ; 
and  they  shoidd  be  swept  by  the  fire  of'  the  enceinte. 

Without  these  precautions,  an  enemy  might  cut  off  all 
communication  from  the  enceinte  with  the  outworks;  and 
in  case  of  retreat,  the  troops  could  not  derive  any  assistance 
from  the  enceinte,  if  he  attempted  to  press  upon  them. 

5.  They  should  be  so  placed  as  not  to  compromise  the  re- 
treat of  the  troops. 

This  is  effected  by  placing  the  communication  in  the  re- 
enterings, which  are  the  most  secure  points ; as  an  enemy 
to  arrive  at  them  will  have  to  brave  a powerful  column  of 
fiank  fire.  Barriers,  gates,  and  movable  bridges  of  timber 
should  be  placed  at  suitable  points,  to  cut  off  one  communi- 
cation from  another;  and  thus  arrest  the  progress  of  a pur- 
suing enemy. 

6.  Finally,  each  loorh  should  be  independent  of  every 
communication,  except  that  one  destined  for  its  particnlar 
use. 

If  this  condition  he  not  fulfilled,  a work  may  sometimes 
be  captured  by  an  enemy  obtaining  possession  of  a com- 
munication passing  through  it,  but  designed  for  the  service 
of  some  other  work. 

36.  Ramps.  The  principal  communications  consist  of 
rarnps,  stairs,  posterns,  gateways,  bridges,  and,  for  wet 
ditches,  dikes.  The  width  of  ramps  at  top  for  the  service 
of  the  artillery  and  other  vehicles  may  be  from  10  to  15 
feet,  and  their  inclination  from  ^ to  or  less,  depending 
on  the  difference  of  level  to  l)e  overcome.  They  are  usu- 
ally placed  in  positions  where  they  will  occupy  the  least 
room  on  the  parade,  as  along  the  rampart  slope  of  the 
enceinte.  As  a general  rule,  their  side  slopes  are  of  earth  ; 
but  where  it  is  desirable  to  economize  room  on  the  parade, 
the  side  slopes  are  replaced  on  one  or  both  sides  by  a wall 
which  sustains  the  earth  of  the  ramp.  When  ramps  serve 


ELEM?:XTS  OF  PERMANENT  FORTIFICATION. 


for  infantry  alone  their  width  may  be  reduced  to  6 feet,  and 
in  some  cases  to  4 feet. 

37.  Stairs.  Except  for  temporary  purposes,  stairs  are 
constructed  of  stone  ; each  step  being  a solid  block  which 
is  6 feet  long  in  the  clear;  its  breadth  at  top  or  the  tread 
12  inches,  and  its  height  or  rise  8 inches.  Stairs  are  usually 
placed  along  the  counterscarp  and  gorge  walls  of  the  out- , 
works,  forming  a communication,  for  infantry  only,  between 
the  ditch  and  the  terre-plein  of  the  work  to  which  they  lead. 
They  are  also  used  within  the  enceinte  in  positions  where 
there  is  not  sufficient  room  for  ramps,  where  bomb-proof 
cover  is  required,  or  where,  for  greater  security  from  sur- 
prise, it  is  desirable  to  present  a narrower  and  more  difficult 
defile  to  the  assailant.  In  cases  where  room  is  wanting,  and 
the  communication  not  in  habitual  use,  the  width  of  the 
stair  may  be  reduced  to  4 feet. 

38.  Posterns.  Posterns  are  arched  bomb-proof  passage- 
ways constructed  under  the  terre-pleins  and  ramparts,  form- 
ing subterranean  communications  between  the  parade  and 
the  enceinte  ditch,  or  between  tlie  ditches  and  the  interior  of 
the  outworks.  The  width  and  height  of  the  interior  of 
posterns  depend  upon  the  use  to  which  the  communication 
is  to  be  applied.  For  artillery  the  width  is  usually  taken  at 
10  feet,  and  the  height  under  the  crown  or  key  of  the  arch 
at  least  8 feet.  Posterns  for  infantry  may  be  only  from  6 
to  4 feet  wide,  and  from  6 feet  6 inches  to  8 feet  high 
under  the  crown  of  the  arch.  The  thickness  of  the  piers  of 
the  arches  is  generally  taken  at  about  half  the  width  of  the 
postern.  The  arches  are  from  2 to  3 feet  thick.  As  any 
injury  to  the  arch  from  the  bursting  of  a shell  over  it  might 
obstruct  the  communication,  the  arch  should  be  covered 
with  a thickness  of  earth  sufficient  to  thoroughly  protect  it. 
A strong  wooden  door  is  placed  at  each  outlet  of  the  postern 
to  secure  it  against  surprise.  The  doorway  in  posterns  for 
the  service  of  artillery  should  be  of  just  sufficient  height  for 
tlie  convenient  passage  of  a gun;  about  7 feet  for  each 
dimension  is  usually  allowed  for  this  purpose. 

The  most  important  postern  is  the  one  leading  from  the 
parade  to  the  enceinte  ditch.  This  generally  receives  a 
width  of  12  feet  and  the  same  height  under  the  crown.  For 
greater  security  from  surprise,  its  outlet  at  the  enceinte 
ditch  is  at  least  6 feet  above  the  bottom  of  the  ditch,  this 
difference  of  level  being  overcome  by  means  of  a temporary 
wooden  ramp  which  receives  an  inclination  of  at  least  -J-. 
With  a like  object,  besides  two  strong  doors  at  the  two  ends 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


33 


of  the  posters,  there  is  a partition  of  masonry  about  mid- 
way between  the  two  ends,  which  is  pierced  with  a doorway 
of  the  same  size  as  the  doorways  of  the  ends,  and  closed  by 
a strong  door  which,  as  well  as  the  partition  wall,  is  loop- 
holed  for  musketry. 

In  cases  where  the  postern  forms  the  main  entrance  to  the 
work,  an  arched  chamber  is  placed  on  one  side  of  it,  at  the 
outlet,  which  serves  as  a guard-room  for  a few  men,  to 
secure  the  outlet  from  surprise.  The  wall  between  this 
chamber  and  the  postern  is  loop-holed,  so  that  a fire  can  be 
brought  to  bear  on  the  doorway  of  the  postern  ; and  as  a 
further  precaution  against  surprise  a machicoulis  defence  is 
sometimes  arranged  at  the  top  of  the  scarp  wall  just  above 
the  doorway  of  the  postern. 

39.  G-ateway.  In  works  with  large  garrisons,  where 
the  means  of  frequent  communication  with  the  exterior  are 
requisite,  posterns  of  ordinary  dimensions  are  found  not  to 
afford  a sufficient  convenience  for  the  daily  wants.  In  such 
cases  a passage-way  of  sufficient  width  to  admit  of  at  least 
a single  carriage-road  with  narrow  foot-paths  on  each  side 
has  to  be  opened  through  the  rampart,  which,  whenever  it 
is  practicable  to  do  so,  should  be  arched  and  covered  with 
earth  to  render  it  bomb-proof.  The  passage-way  should 
for  security  have  the  bottom  of  its  outlet  at  least  twelve 
feet  above  the  bottom  of  the  enceinte  ditch ; and  when 
this  difference  of  level  cannot  be  obtained  the  main  ditch 
should  be  deepened  sufficiently  for  the  pur])ose  below  the 
outlet.  A gateway  of  sufficient  height  and  width  for  the 
passage  of  the  ordinary  vehicles  for  the  service  of  the  gar- 
rison is  made  through  the  scarp-wall.  This  gateway  is 
arched  at  top,  where  a machicoulis  defence  may  also  be 
arranged  to  guard  the  outlet  on  the  exterior. 

The  communication  across  the  enceinte  ditch  leading  from 
the  gateway  is  usually  an  ordinary  wooden  bridge  built  on 
piles.  The  bay  of  this  bridge  at  the  gateway  is  spanned  by 
a drawbridge  of  timber,  wliicdi  when  drawn  up  closes  and 
secures  the  gateway.  This  drawbridge  is  manoeuvred  by 
some  of  the  usual  mechanisms  employed  for  this  purpose. 

40.  Port-Cullis.  When  tl  le  gateway  is  not  preceded 
by  a ditch,  and  is  therefore  without  a drawbridge,  a barrier, 
termed  port-cuUis^  which  can  be  lowered  or  raised  verri- 
cally  by  machinery,  is  sometimes  added  to  secure  the  pas- 
sage-way from  surprise.  The  ancient  port-cullis  was  a 
framework  of  heavy  beams,  placed  vertically,  leaving  a few 
inches  only  between  each  pair  of  beams.  These  vertical 

3 


34 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


beams  were  either  solidly  confined  between  horizontal 
beams,  or  clamping  pieces  in  pairs;  or  else  they  were  so 
arranged  that  they  conld  slide  upwards  between  the  clamp- 
ing-pieces. Eacli  of  the  vertical  beams  was  shod  at  the 
bottom  with  a strong-pointed  iron  shoe.  The  horizontal 
pieces  were  framed  securely  with  two  heavy  vertical  beams 
that  formed  the  sides  of  the  frame,  and  were  fitted  into 
vertical  grooves  made  in  the  side  walls  of  the  passage-way 
in  which  the  frame  could  slide  when  raised  or  lowered.  By 
arranging  the  vertical  beams  to  slide  upwards  between  the 
clamping  pieces,  it  enabled  the  passage-way  to  be  closed  in 
cases  where  an  obstruction  might  be  designedly  placed  be- 
low the  port-cullis  to  prevent  this  being  done  ; as  the  beams 
which  meet  the  obstruction  would  be  pushed  upwai’ds, 
wiiiist  the  others  would  fall  to  their  ordinary  level  and  close 
the  passage  way  on  each  side  of  the  obstruction. 

In  the  works  recently  constructed  with  us  the  port-cullis, 
and  even  the  doors  preceding  them  have,  been  constructed 
of  a strong  open  lattice-work  of  wrought-iron  bars  bolted 
strongly  to  the  wrought-iron  uprights  and  cross  pieces, 
forming  the  framework  of  the  lattice.  This  is  a great  im- 
provement for  these  purposes,  both  as  to  durability  and  de 
fence. 

Passage-ways  of  this  description  should  be  secured  by  all 
the  means  at  an  engineer’s  disposal.  A large  guard-room, 
wdth  loop-holes  bearing  on  the  passage,  should  be  erected  on 
one  side,  near  the  gateway  ; and  if  the  enceinte  is  a simple 
one,  without  outworks  beyond  its  ditch,  a small  lunette,  or 
redan,  should  be  constructed  beyond  the  counterscarp,  form- 
ing a tete-de-pont,  for  the  security  of  the  bridge  from  sur- 
prise, and  which  in  connection  with  the  glacis  protects  it 
from  artillery  and  infantry  fire. 

The  drawbridge,  which  for  convenience  of  manoeuvring 
should  not  be  longer  than  12  feet,  is  constructed  in  the 
usual  mode. 

When  passages  through  the  ramparts  are  provided  for 
railroads,  the  necessary  openings  are  made,  the  ditch  is 
crossed  by  a bridge,  usually  arched  or  of  iron,  with  a draw 
span,  and  all  possible  precautions  are  taken  to  prevent  these 
openings  from  becoming  weak  points  in  the  defence. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


35 


YI. 

ENCEINTES. 

41.  The  most  simple  mode  of  fortifying  a position  in  a 
permanent  manner  consists  in  inclosing  it  with  a rampart 
surmounted  by  a parapet,  with  a ditch  the  scarp  of  which 
when  dry  is  revetted  with  masonry,  and  so  covered  by  an 
earthen  mask  that  it  cannot  be  breached  except  by  batteries 
placed  on  the  border  of  the  counterscarp. 

This  line  of  fortification  enclosing  the  position  is  termed 
the  enceinte^  the  body  of  the  jjlace  or  the  main  inclosure. 

The  general  outline  of  the  enceinte  may  be  curmlinear^ 
or  a polygonal  figure  of  any  character. 

42.  System  of  Fortification.  Although  an  infinite 
diversity  of  figures  may  thus  be  presented  in  the  outline  or 
plan  of  the  enceinte,  they  may  all  be  classed  under  four 
heads,  to  each  of  which  engineers  generally  have  applied 
the  term  system  of  fortification. 

These  four  classes  are,  1,  the  circular  or  curvilinear 
system  ‘ 2,  the  polygonal  or  cagmnniere  system ; 3,  the 
tenanted  system  • 4,  the  hastioned  system. 

The  term  method  of  fortification  is  now"  usually  applied 
to  the  manner  of  fortifying  which  is  generally  prevalent 
in  any  country  ; or  to  the  mode  adopted  by  any  individual, 
as  the  German  method  ; Vauban^s  methof  etc. 

Circular  System.  The  circular  system  consists  of  an 
enceinte,  the  plan  of  which  is  circular  or  curvilinear. 

Polygonal  System.  In  the  polygonal  system  the  plan 
is  either  a polygon  with  salient  angles  alone,  PI.  8,  Fig. 
72,  each  side  of  wdiich,  a a,  is  fianked  by  a casemated  capon- 
niere,  c,  placed  in  the  ditch,  d,  and  midway  betw^een  the 
two  salients,  a ; or  else  each  side  of  the  polygon  is  broken 
, inw"ards  at  the  centre,  so  as  to  form  a slight  reentering,  PI. 
8,  Figs.  73,  74,  75,  76,  77,  to  procure  a casemated  fianking 
arrangement,  f f,  for  the  caponnieres,  c,  which  occu])y 
these  reenterings,  and  also,  in  some  cases,  to  flank  works  in 
advance  of  the  enceinte. 

Tenailled  System.  The  tenailled  system,  PI.  8,  Fig. 
78,  consists  of  a tenailled  line,  the  reentering  angles  of 
which  are  between  90°  and  100°,  and  the  salient  angles  not 
less  than  60°. 


3G 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


Bastioned  System.  In  the  bastioned  system,  Fi^.  Y9,. 
the  bastion  usually  consists  of  two  faces  and  two  flanks,  the 
scarps  of  each  of  which  are  plane  surfaces. 

In  many  of  the  older  fortiflcations,  and  in  a few  of  the 
more  recent  w’orks  in  Europe,  the  flank  is  broken  ; the  por- 
tion of  it  at  the  shoulder  angle  forming  a projecting  mass 
which  is  termed  an  orlllon^  whil't  the  portion  between  the 
orillon  and  the  enceinte  curtain  is  retired,  or  brought  in 
towards  the  interior  of  the  bastion,  and  is  thus  partially 
covered  by  the  orillon  from  Are,  except  in  the  prolongation 
of  the  enceinte  ditch.  In  some  cases  the  plan  of  the  orillon 
as  well  as  that  of  the  retired  flank  is  curvilinear;  in  others 
they  are  both  rectilinear. 

43.  General  Remarks.  Whatever  system  may  be 
adopted  for  the  enceinte,  there  are  certain  conditions,  in 
addition  to  those  already  laid  down  for  all  permanent  works^ 
which  it  must  satisfy  to  render  it  effective : 

1.  It  should  have  a steep  revetted  scarp ; unbrohen  on 
all  sides  except  for  the  necessary  openings  for  communica- 
tions ; thorougJdy  flanked  throughout  by  cannon  and 
small-arms  ; and  of  suflicient  height  to  prevent  all  ordinary 
attempts  at  escalade. 

2.  The  scarp  should  be  so  covered  by  earthen  or  other 
niaslis  that  it  cannot  be  reached  by  the  projectiles  of  an  as- 
sailant from  any  piosition  exterior  to  these  masks. 

3.  The  pamapet  and,  interior  covered  shelters  should  be 
proof  against  solid,  and  hollow  loaded  projectiles. 

d.  The  parapet  should  command  all  the  site  and  out- 
works exterior  to  the  enceinte  and  mithin  range  of  its  guns, 
and  sweep  them  with  front,  flank , and  cross-jires  when  pos- 
sible. 

5.  As  far  as  practicable,  the  jyrincijxd  lines  of  the  para- 
pet should  receive  such  directions,  that  the  assailant  can- 
not take  up  positions  to  enfllade  them. 

Every  enceinte,  whatever  be  the  system  adopted,  will  be 
more  or  less  effective  as  these  conditions  are  more  or  less 
complied  with  in  its  arrangement. 


YII. 


OUTWORKS. 


44.  A work  consisting  of  an  enceinte  alone  is  more  or 
less  exposed  to  surprise,  as  it  must  have  outlets  of  some 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


37 


■description  to  keep  up  a communication  with  the  exterior, 
and  a bridge,  or  other  means  for  crossing  the  ditch. 

But  this  is  not  the  only  defect  of  a fortification  of  this 
simple  character;  for  having  no  covers  beyond  the  ditch 
for  its  garrison,  their  action  must  be  restricted  to  what  may 
be  termed  a passive  resistance  alone ; in  any  attempt  to 
0})erate  on  the  exterior,  they  are  exposed  to  fire  as  soon  as 
they  emerge  from  the  ditch,  and  in  a retreat  towards  the 
work,  if  closely  pursued  by  the  assailant,  they  will  not  only 
run  the  risk  of  being  cut  off,  but  a retreat  under  such  cir- 
cumstances may  lead  to  the  capture  of  the  work  itself,  by 
the  assailant  being  enabled  to  enter  it  with  the  retreating 
force. 

To  provide  against  dangers  of  so  grave  a character,  engi- 
ueers  have  devised  other  defences  beyond  the  ditch,  and 
which  they  have  placed  in  immediate  defensive  relations 
with  the  enceinte,  being  under  its  fire,  and  in  positions 
where,  if  assaulted,  they  can  be  readily  succored  by  the  gar- 
rison. To  this  class  of  exterior  defences  the  term  outworhs 
has  been  applied. 

From  their  position,  exterior  ro  the  enceinte,  and  from 
their  angular  form,  so  as  to  be  fianked  by  it,  the  outworks, 
wnth  the  enceinte,  form  salient  ana  reentering  parts,  which 
are  very  favorable  to  the  security  of  sortie  parties  in  re- 
tiring; and  as,  if  properly  arranged,  the  assailant  must  take 
them  in  succession,  they  will  greatly  prolong  the  defence,  by 
forcing  him  to  a great  development  of  his  trenches;  through 
which,  in  some  of  the  positions  he  will  be  obliged  to  occupy, 
be  will  be  the  enveloped  party.  Besides  this,  he  will  be 
obliged  to  establish  breach  batteries  against  each  work  in 
succession — always  a difficult  and  perilous  task. 

45.  The  outworks  should  satisfy  the  following  conditions 
to  render  them  effective  and  secure  : 

1.  They  should  have  revetted  scarps  of  sufficient  height 
to  secure  them  from  any  ordinary  open  assault. 

2.  As  far  as  practicable  their  scarps  should  be  flanked 
by  the  enceinte,  and  be  masked  from  the  positions  of  the 
assailants  batteries. 

3.  Their  parapets  and  covered  shelters  should  be  shot- 
proof. 

4.  Those  which  are  most  retired  should  command  those 
in  advance;  and  whenever  this  cannot  be  done^  the  re- 
tired work  should  be  defied  from  the  one  in  advance  by 
which  it  is  commanded. 

5.  In  any  combination  of  outworks  the  dispositions 


38 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


should  he  such  that  the  more  advanced  ones  shall  fall  into 
the  hands  of  the  assailant  before  he  will  he  able  to  gain  pos- 
session of  the  more  i^etired. 

6.  The  commtinications  should  he  ample^  and  satisfy  the 
general  conditions  for  these  elements. 

46.  The  works  which  come  under  this  head  are  the 
covered-way.,  the  tenaille^  the  demi-lune,  the  counterguard, 
the  redoubt  or  reduit^  the  tenaillon^  the  horn-worlc^  and  the 
crown-work. 

47.  Covered-Way.  The  covered-way,  as  its  name  im- 
ports, is  an  open  corridor  or  passage,  masked  from  the  as- 
sailant’s view  by  an  embankment,  which  borders  the  ditch 
of  tlie  enceinte  alone  when  there  are  no  other  outworks 
but,  in  the  contrary  case,  also  envelops  the  ditches  of  these, 
forming  thus  a continuous  covered  line  of  communication 
around  the  fortification. 

The  covering  embankment  itself  is  arranged  towards  the 
covered-way  like  an  ordinary  parapet,  and  it  receives  on  the 
exterior  a gentle  slope  or  glacis. 

By  this  arrangement  the  garrison  have  a covered  position 
beyond  the  ditch  where  they  can  assemble  with  safety  either 
for  the  purpose  of  making  a sortie,  or  to  guard  the  ditches 
and  the  communications  across  them ; and  which  affords 
them  also  a secure  point  of  retreat  if  repulsed  in  a sortie,  as 
a reserve  left  in  the  covered-way  will  be  at  hand  to  check 
the  pursuit  by  their  fire,  and  enable  the  retreating  party  to 
gain  the  enceinte. 

48.  Place s-of- Arms.  The  covered-way  from  the  direc- 
tion given  to  the  counterscarps  of  the  enceinte  and  out- 
works, forms  a line  of  communication  wdth  salient  and  re- 
entering parts.  Pis.  8,  9,  Figs.  80  to  85. 

The  salient  portions,  s,  are  termed  salient  places-of-arms  / 
and  the  reentering  parts  the  reentering  places-of-arms. 

The  salient  places-of-arms,  it  will  be  seen,  result  from  the 
general  plan  of  the  covered-way  ; but  the  reentering  places- 
of-arms  are  formed  by  changing  the  directions  of  the  two 
branches  where  they  form  the  reenterings,  r,  so  as  to 
make  a salient  within  the  reenterings;  thus  enlarging  the 
covered-way  at  these  points  and  producing  a flanking  ar 
rangement,  by  which  the  glacis  can  be  swept,  and  a cross-fire 
be  brought  to  bear  on  the  ground  in  advance  of  the  salients. 

49.  Traverses.  The  covered-way,  from  its  position, 
and  the  usually  slight  command  given  to  the  crest  of  its 
glacis,  is  very  much  exposed  to  the  effects  of  an  enfilading 
fire. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


39 


With  a view  to  remedy  this  defect,  and  also  to  enable 
the  garrison  to  dispute  foot  by  foot  the  possession  of  this 
outwork  by  the  assailant,  earthen  masks,  formed  like  an 
ordinary  parapet  and  termed  traverses^  are  thi  own  np  across 
it.  The  traverses  usually  extend  to  the  counterscarp,  the 
wall  of  which  is  built  up  to  sustain  them. 

At  the  end,  towards  the  glacis,  a passage,  or  defile,  is  left  • 
between  them  and  the  covering  embankment,  to  admit  of  a 
free  communication  throughout  the  covered-way. 

50.  Tenaille.  The  tenaille  is  a low  work  placed  in  the 
reentering  formed  in  the  enceinte  ditch  by  the  curtain  and 
flanks  of  the  bastioned  system,  being  isolated  by  a ditch 
between  it  and  these  parts  of  the  enceinte.  Its  chief  pur- 
pose is  to  serve  as  a mask,  covering  the  scarp  walls  of  this 
reentering  from  fire,  as  well  as  the  outlets  to  the  enceinte 
ditch,  which  are  usually  placed  in  the  centre  of  the  curtains. 

The  tenaille  has  received  various  forms  from  engineers. 
In  some  cases  it  has  been  made  with  two  faces  or  wings, 
making  a reentering  angle  opposite  the  centre  of  the  en- 
ceinte curtain.  In  others  the  two  wings,  instead  of  being 
prolonged  until  they  meet,  are  connected  by  a short  curtain 
parallel  to  that  of  the  enceinte.  In  some  examples  it  has 
the  form  of  a small  bastioned  front.  In  others  it  consists 
of  two  flanks  connected  by  a curtain.  These  flanks  in  some 
cases  have  been  casemated  for  guns  and  mortars.  The 
tenaille  is  usually  revetted  with  masonry  both  in  front  and 
rear.  In  some  cases  the  ends  alone,  towards  the  flanks  of 
the  enceinte,  are  revetted,  the  intermediate  portions  con- 
sisting of  an  ordinary  earthen  parapet  without  either  scarp 
or  gorge  wall. 

51.  Demi-lune.  The  demi-lune.  PI.  9,  Figs.  81,  82.  83, 
81:,  is  a work  in  the  form  of  a redan,  d,  placed  in  front  of 
the  enceinte  curtain,  which  it  masks  from  lire,  as  well  as  a 
portion  of  each  face  of  the  enceinte,  at  the  shoulder  angles 
of  the  bastions.  It  is  isolated  from  the  enceinte  by  the 
main  ditch.  From  its  importance  the  scarp  and  gorge  of 
the  demi-lune  are  generally  revetted,  though  in  some  cases 
the  revetment  has  been  omitted. 

This  work  is  also  called  the  ravelin. 

52.  Counterguard.  The  counterguard  is  an  isolated 
work,  c.  Fig.  80,  in  the  form  of  a redan,  which  envelops  the 
faces  of  a bastion  or  other  salient.  In  Some  cases  it  con- 
sists simply  of  an  earthen  mask  having  the  profile  of  an 
ordinary  parapet ; but  it  is  usually  revetted  both  in  front 
and  rear. 


40 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


53.  Redoubts.  The  term  redoubt,  or  is  ap- 

plied to  outworks  placed  within  other  outworks ; their  object 
lieing  to  strengthen  the  defence  of  the  principal  work. 

A work  of  this  class  is  usually  placed  within  the  demi- 
lune, and  is  termed  the  demi-lune  redoubt.  Small  works 
of  this  kind  are  also  placed  in  the  salient  and  reentering 
places-of-arms  of  the  covered-way,  and  are  termed  the  re- 
doubt of  the  salient.,  or  reentering  ylace  of  arms.  These 
redoubts  are  in  some  cases  simple  earthen  works ; in  others 
they  are  revetted;  and  in  others  casemated  both  for  the 
service  of  artillery  and  small-arms. 

54.  Tenaillon.  The  term  tenaillon,  PI.  9,  Fig.  81,  is 
applied  to  a kind  of  face  cover,  or  counterguard,  t,  of  the 
demi-lune.  It  is  only  to  be  met  with  in  some  of  the  old  for- 
tified places  of  Europe,  and  was  added  to  give  more  strength 
to  fronts  where  the  demi-lune  was  too  small. 

55.  Horn-Work.  The  horn -work,  PI.  9,  Fig.  82,  usually 
consists  of  a bastioned  front,  h,  with  the  ordinary  outworks, 
having  two  long  branches,  f f,  or  wings,  which  rest  upon 
two  adjacent  bastions,  or  two  adjacent  demi-lunes,  dd,  of 
the  enceinte ; its  covered-way  forming  with  that  of  the 
enceinte  a continuous  line  of  communication.  The  object 
of  this  outwork  is  to  strengthen  a salient  or  other  weak  por- 
tion of  the  enceinte. 

56.  Crown-Work.  The  crown-work,  PI.  9,  Fig.  83, 
consists  of  two  or  more  bastioned  fronts,  c,  with  their  out- 
works, placed  in  front  of  some  portion  of  the  enceinte,  to 
give  it  additional  strength.  It  is  terminated  like  the  horn- 
work  by  two  wings,  ff,  which  rest  either  upon  the  enceinte, 
or  upon  two  demi  lunes,  dd.  Its  covered-way,  like  that  of 
the  horn-work,  forms  a continuous  communication  with  that 
of  the  enceinte. 

YIII. 

ADVANCED  AND  DETACHED  WORKS. 

57.  The  term  advanced  worhs  is  applied  to  such  works 
as,  placed  beyond  the  outworks,  are  still  in  defensive  rela- 
tions with  them  and  the  enceinte,  by  being  so  brought 
under  the  fire  of  either  the  enceinte  or  the  outworks  that 
the  ground  in  advance  of  them  will  be  swept  by  this  fire; 
their  ditches  flanked  by  it;  and  their  interior  so  exposed  to 
it  that,  if  the  work  were  seized  by  an  open  assault,  the 
assailant  could  be  driven  from  it  by  this  fire. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


41 


They  are  usually  in  the  form  of  redans  or  lunettes,  and 
in  some  cases  horn  and  crown  works,  depending  on  the  ex- 
tent of  ground  that  it  may  be  thought  necessary  to  occupy 
with  them. 

58.  Advanced  works  are  placed  in  positions  which  the 
assailant  must  necessarily  make  himself  master  of  before  he 
can  approach  nearer  to  the  main  work  ; or  on  points  which 
overlook  ground  that  cannot  be  swept  by  the  tire  of  the 
enceinte;  and  sometimes  on  points  which,  inaccessible  to 
the  assailant,  give  good  position  from  which  a flank  fire  can 
be  brought  to  bear  upon  ground  over  which  the  assailant 
will  be  obliged  to  make  his  approaches. 

Restricted  to  these  purposes,  an  advanced  work  may  be  of 
great  value  in  prolonging  the  defence;  and  every  precau- 
tion should  be  taken  to  secure  the  work  from  a surprise, 
and  to  give  its  garrison  a safe  means  of  communication  with 
the  outworks  upon  which  they  can  retire  when  forced  to 
abandon  their  work. 

In  works  of  great  extent,  with  full  and  strong  garrisons, 
advanced  works,  by  judicious  combination  with  the  works 
in  tbeir  rear,  may  greatly  enlarge  the  field  of  action  of  the 
garrison;  keeping  the  assailant  at  a distance,  and  annoying 
him  by  frequent  sorties  in  large  bodies,  made  under  the 
protection  of  the  outworks. 

In  Plate  9,  Fig.  84,  is  an  advanced  work,  l,  flanked  by 
the  demi-lunes,  d,  of  the  enceinte.  The  plan  of  this  work  is 
R lunette  with  its  covered-way  and  places-of-arms,  e and  s. 

59.  Detached  works  are  those  which,  although  having  an 
important  bearing  on  the  defence  of  the  main  work,  are  so 
far  from  it  as  to  have  to  depend  solely  on  their  own  strength 
in  case  of  assault. 

Depending  solely  on  their  own  strength,  they  should  have 
a revetted  scarp  and  counterscarp  of  sufficient  height  to  pre- 
sent great  difficulties  to  an  open  assault,  and  have  their 
ditches  flanked  either  from  the  parapet  of  the  work  itself  or 
by  caponnieres  or  by  counterscarp  galleries. 

Detached  works  may  be  either  of  a polygonal  or  bastioned 
form,  depending  upon  the  extent  of  ground  to  be  occupied  ; 
the  former  being  more  suitable  to  small  works  to  which  the 
bastioned  form  does  not  lend  itself. 

They  belong  to  the  class  of  works  termed  fo7'ts,  as  dis- 
tinguished from  fortresses. 

They  are  used  to  occupy  ground  like  commanding  heights, 
which,  although  not  within  good  sweep  of  the  fire  of  the 
main  work,  is  still  within  range  of  the  heaviest  calibres  of 


42 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


the  assailant,  and  which  if  occupied  by  him  would  prove  a 
source  of  serious  annoyance  to  the  work. 

The  more  favorite  mode  now  among  engineers  for  the  de- 
fensive works  of  cities  is  to  enclose  them  with  a continuous 
enceinte  of  sufficient  strength  to  repel  an  open  assault,  or 
to  retain  this  enceinte  if  it  already  exists  and  to  occupy 
positions  in  advance  of  the  main  work,  beyond  extreme 
cannon-range,  by  a line  of  forts  so  strong  that  they  can  only 
be  reduced  by  regular  siege,  and  so  placed  that  one  or  more 
must  be  taken  before  the  assailant  can  approach  the  main 
work.  In  some  cases  a second  line  is  established  outside' 
the  lirst,  and  the  whole  area  within  the  exterior  cordons 
partakes  of  the  nature  of  an  intrenched  camp. 


IX. 

INTERIOR  RETRENCHMENTS. 

60.  Besides  the  works  exterior  to  the  enceinte,  the  object 
of  which  is  to  retard  the  assailant  in  his  attempts  to  enter 
it  l)v  breaching,  engineers  have  placed  within  it  other  works 
which,  in  some  cases,  are  designed  simply  to  enable  the 
garrison  to  make  an  effectual  defence  of  the  breach,  when 
the  assault  upon  it  is  made,  and  give  them  a secure  point  of 
retreat  and  safety  when  driven  from  it  ; and  in  others  these 
interior  works  are  chiefly  designed  to  bring  plunging  Are  to 
bear  on  the  assailant’s  siege  works  exterior  to  the  enceinte. 
The  former  class,  intended  for  the  defence  of  the  breach 
alone,  are  termed  interior  retrenchments;  and  the  latter 
cavaliers. 

61.  Interior  retrenchments  in  the  bastioned  system  are. 
either  placed  within  the  bastions,  which  are  the  parts  of  the. 
enceinte  usually  breached,  or  in  rear  of  their  gorges.  Those 
which  are  placed  within  the  bastions  extend  across  them_ 
either  between  the  faces  or  between  the  flanks.  When  placed 
at  the  gorge  they  connect  the  two  adjacent  curtains. 

The  plan  of  these  works  varies  with  their  position,  the 
size  of  the  bastions,  or  the  more  or  less  openness  of  their 
salient  angles. 

In  small  bastions  with  acute  salients,  when  the  retrench- 
ment rests  upon  the  faces,  it  usually  receives  the  form  of  a 
tenaille  or  inverted  redan,  tbe  angle  of  the  tenaille  being 
about  100°.  When  the  bastions  are  large  and  the  salient 
angle  quite  open  or  obtuse,  the  retrenchment  may  receive; 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


43 


the  form  of  a small  bastion^ front,  PL  9,  Fig.  85,  resting 
upon  the  faces. 

Either  of  these  forms  may  in  like  manner  be  used,  when 
the  retrenchment  rests  upon  the  flanks  of  the  bastion.  But 
as  this  position  enables  a retrenchment  of  the  form  of  an 
ordinary  redan  to  have  its  ditches  swept  by  the  tire  of  the 
flanks  of  the  adjacent  bastions,  this  form  is  in  some  cases 
used  in  preference. 

When  placed  between  two  curtains  at  the  gorge  of  a 
bastion  the  plan  of  the  retrenchment  is  always  a bastioned 
front. 

In  the  polygonal  system,  until  within  a few  years,  the  in- 
terior retrenchments  were  high  casemated  defensive  bar- 
racks or  keeps  arranged  to  Are  over  the  parapet  from  their 
upper  tiers,  and  to  sweep  the  terre-pleins  and  parade  from 
their  lower  ones.  They  are  now  made  of  less  height  and 
their  masonry  is  covered  from  Are,  forming  bomb-proof  de- 
fensive barracks  as  previously  described. 

62.  Cavaliers  are  placed  either  upon  the  curtains  or  within 
the  bastions.  The  latter  is  the  more  usual  position  selected 
for  them.  Their  plan  in  this  position  is  usually  that  of  a 
lunette,  the  faces  and  flanks  of  which  are  parallel  to  those 
of  the  enveloping  bastion.  Cavaliers  receive  a considerable 
command  over  the  parapet  of  the  enceinte,  and,  in  some 
cases,  they  are  arranged  with  a tier  of  casemated  Are,  above 
which  is  an  open  battery. 

In  polygonal  works  the  cavaliers  are  generally  placed  at 
the  salients  and  in  the  middle  of  the  faces,  when  they  are 
long,  protecting  the  faces  from  enfllade  and  affording  cover 
for  magazines  and  quarters,  as  well  as  giving  a plunging 
Are  on  the  ground  in  front.  In  some  large  and  important 
works  it  is  proposed  to  provide  them  with  iron  or  steel 
turrets. 

Interior  retrenchments  and  cavaliers  are  usually  construct- 
ed with  a revetted  scarp  and  counterscarp  to  secure  them 
from  an  open  assault ; and,  in  some  cases,  a covered-way, 
wdth  a small  reentering  place-of-arms,  r,  PL  9,  Fig.  85, 
closed  by  traverses,  is  arranged  in  advance  of  the  ditch,  to 
insure  the  safe  retreat  of  the  garrison  when  driven  from  the 
breach. 


44 


ELEMENTS  OP  PEilMANENT  FORTIFICATION. 


CHAPTEK  II. 

SYSTEMS  OF  FORTIFICATION. 

In  the  discussion  of  the  relative  merits  of  different  systems 
of  fortification,  their  capacity  to  resist  the  close  attack  of  the 
besiegers  formerly  had  the  greatest  weight. 

Modern  methods  have  given  to  the  distant  attack  a value 
and  efficiency  much  greater  than  it  formerly  had ; so  great 
that  in  some  cases  it  alone  determines  the  result  of  the 
siege. 

The  conduct  of  recent  sieges,  notably  that  of  Strasburg 
in  1870,  in  which  the  close  attack  was  pushed  up  to  occupy^ 
ing  the  advanced  works,  crowming  the  covered-way,  and 
breaching  the  main  enceinte’  have  shown,  however,  that  the 
close  attack  may  not  be  entirely  a thing  of  the  past,  and 
that  proper  dispositions  to  meet  it  must  still  be  made.  The 
relative  advantages  of  the  different  systems  must  then  be 
determined,  not  only  by  the  character  of  the  site  and  size  ot 
the  work,  but  also  by  the  probable  nature  of  the  attack  and 
defence,  and  the  other  considerations  which  arise  in  each 
particular  case. 


I. 

BASTIONED  SYSTEM. 

63.  A bastioned  enceinte  consists  of  a series  of  bastions 
which  occupy  the  salient  angles  of  the  polygon  within  wdiich 
the  enceinte  is  inclosed  ; the  flanks  of  the  bastions  being 
usually  connected  by  straight  curtains. 

The  sides  of  the  polygon  which  connect  the  salient  angles 
of  the  bastions  are  termed  the  exterior  sides^  in  contradis- 
tinction to  the  sides  of  an  interior  polygon  which,  being 
parallel  to  the  first  and  occupying  the  positions  of  the  cur- 
tains, are  termed  the  interior  sides. 

The  bastioned  enceinte,  when  its  relief  and  plan  are 
suitably  arranged,  possesses  the  advantage  of  having  its 


ELEMENTS  OF  PERMANENT  FORTIFICATION.  45 

/ 

ditclios  thoroughly  swept  from  within  the  enceinte  itself, 
thus  securing  the  flanking  arrangement  of  the  scarp ; of 
bringing  a cross  and  flank  fire  to  bear  upon  the  approaches 
on  the  salients  of  the  enceinte,  and  furnishing  a strong 
direct  and  cross  fire  upon  the  site  in  advance  of  the  curtains 
and  the  faces  of  the  bastions. 

64.  The  principal  objections  urged  against  the  bastioned 
system  are : 

1.  That  its  chief  characteristic,  a perfect  flanking  disposi- 
tion for  the  entire  line  of  the  scarp,  is  attainable  only  under 
certain  relations  between  the  requisite  relief  for  a permanent 
work  and  the  lengths  of  the  exterior  side  and  curtain,  which 
therefore  restricts  it  in  its  application  to  fortifications  in 
which  these  relations  exist. 

2.  That,  in  order  to  secure  a sufficient  length  of  flank  for 
an  effective  flanking  disposition,  the  angle  between  the  face 
of  the  bastion  and  the  exterior  side,  termed  the  dirninished 
angle  of  the  polygon,  has  to  be  made  so  great  as  to  decrease 
considerably  the  space  inclosed  within  the  polygon,  whilst 
the  development  of  the  line  of  the  enceinte  is  greatly  in- 
creased by  it. 

3.  That  the  direction  necessarily  giv^en  to  the  faces  from 
this  cause  throws  their  prolongations  in  positions  very  favor- 
able to  the  erection  of  enfilading  batteries  against  them. 

4.  That  the  flanks,  upon  which  the  whole  system  is  based, 
lie  in  positions  in  which,  like  the  faces,  they  can  be  not  only 
easily  enfiladed,  but  are  further  exposed  to  a reverse  fire 
from  shot  which  may  pass  over  the  parapet  of  the  faces  as 
well  as  the  opposite  flank,  or  even  to  being  breached  by  fire 
intended  only  to  enfilade  the  face  in  their  front. 

5.  And  that  these  objections  are  the  stronger  as  the  sali- 
ent angles  of  the  polygon  are  smaller  or  as  the  number  of 
sides  is  decreased. 

6.  That  by  reason  of  objections  3 and  4,  the  artillery  of 
the  faces,  flanks  and  demi-lune  is  not  able  to  withstand  the 
distant  enfilade  fire  of  the  besieger,  and  in  consequence  it 
has  little  or  no  value  in  retarding  his  approach  until  the 
third  parallel  is  reached,  when  this  distant  fire  ceases  in  ordei 
to  avoid  injuring  his  own  men. 

That  this  fact  reduces  the  value  of  the  artillery  defence  to 
a minimum,  and  restricts  the  size  of  the  fronts  to  those  wfiicii 
can  be  defended  by  infantry  fire. 

Besides  these  objections,  which  to  a certain  extent  are  well 
founded,  where  the  defensive  arrangements  are  chiefly  open. 


46 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


as  is  the  case  in  most  land  fronts,  others  have  been  urged 
against  this  system,  which,  being  rather  of  a comparative 
character,  as  showing  the  advantages  of  other  systems  over 
this,  will  best  be  examined  elsewhere. 


II. 

VALTIAn’s  first  METHODo 

65.  Yauban,  born  1632,  died  1707,  has  left  examples  of 
three  different  methods  in  the  places  planned  by  him.  The 
fortress  of  'New  Brisac  is  fortified  after  his  third  method  ; 
those  of  Landau  and  Belfort  after  his  second  ; but  the  greater 
part  of  the  places  fortified  by  him  are  planned  according  to 
his  first  or  earliest  method. 

66.  Profile  of  Enceinte.  In  the  profile  of  this  method. 
Fig.  1,  Pi.  10,  the  scarp  wall  is  36  feet  high,  its  slope  being 
five  perpendicular  to  one  of  base ; surmounting  this  is  an- 
other wall  from  4 to  6 feet  high,  the  object  of  which  is  to 
sustain  the  exterior  of  the  parapet.  The  parapet  i^  18  feet 
thick,  the  superior  slope  being  ^ ; the  interior  crest  is  8 
feet  above  the  terre-plein,  which  is  42  feet  in  widifch.  The 
mean  command  of  the  interior  crest  above  the  site  is  about 
26  feet.  The  bottom  of  the  ditch  is  about  17^  feet  below 
the  site. 

67.  Plan  of  Enceinte.  Yauban  adopted  no  arbitrary 
or  invariable  combination  of  parts  in  his  methods.  His 
great  excellence  as  an  engineer  is  shown  in  the  skill  with 
which  he  adapted  the  fortifications  he  planned  to  the  de- 
fensive requirements  of  the  sites;  selecting  long,  medium, 
or  short  exterior  sides,  and  varying  the  length  and  directions 
of  tlie  faces  and  fianks  so  as  to  procure  the  best  command 
over  the  exterior  ground,  and  to  withdraw  these  parts  from 
the  enfilading  fire  of  the  assailant. 

In  his  works,  however,  he  has  generally  taken  360  yards 
as  the  greatest  limit  of  the  exterior  side ; the  perpendicular 
of  the  front  ^ when  the  polygon  is  a square ; 
pentagon  ; and  ^ for  all  higher  polygons.  / 

With  these  starting-points  he  procured  diminished  angles 
which  gave  more  than  60°  to  the  salient  angles  of  the  bas- 
tions in  all  cases,  and  flanks  of  suitable  length  both  to  flank 
the  main  ditch  and  to  encounter  wfith  advantage  the  counter 
batteries  which  could  be  erected  against  them. 

The  following  constructions  both  for  the  enceinte  and 


i 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


47 


outworks  are  taken  from  tbe  best  French  authorities  as 
adopted  by  him  for  polygons  higher  than  the  pentagon. 

68.  In  the  plan  of  trace  (Fig.  2,  PI.  10),  the  magistral  is^ 
taken  as  the  directing  line;  the  exterior  side  is  360  yards; 
on  the  perpendicular  of  the  front  a distance  of  ^ the  exterior 
side  is  setjiff;  lines  drawn  through  this  point  and  the  ex- 
tremities of  the  exterior  side,  determine  the  directions  of 
tiie  faces,  and  the  lines  of  defence ; from  the  salients  a dis- 
tance equal  to  f of  the  exterior  side  is  set  off,  wdiich  gives 
the  lengths  of  the  faces  and  the  positions  of  the  shoulder 
angles  ; the  ffank  is  drawn  by  taking  the  opposite  shoulder 
angle  as  a centre,  and  with  a radius  equal  to  the  distance 
between  the  shoulder  angles  describing  an  arc  to  inter- 
sect the  line  of  defence/;  the  chord  of  this  arc  is  the  flank  ; 
the  curtain  is  drawn  by  joining  the  extremities  of  the  flanks. 
By  this  construction  the  flanks  will  be  about  54  yards  ; tlie 
curtain,  146  ; and  the  lines  of  defence,  26Y ; the  length  of 
these  being  determined  so  that  the  salients  of  the  bastions 
can  be  defended  with  the  rampart  gun^  or  wall-piece. 

69.  Tenaille.  In  many  oi  the  places  constructed  before 
Yauban’s  time  there  was  Si  fausse-hraie,  enveloping  the 
enceinte  and  connected  with  it.  This  work  was  suppressed 
by  Yauban,  who  was  the  first  to  ifse  ^ip-^npUein  its  place. 

The  tenaille  is  separated  from  curtain  by  a ditch  10 
yards  wide,  and  from  the  flanks  by  ditches  of  6 yards. 

The  form  of  the  tenaille  as  used  by  Yauban  was  variable. 
In  some  cases  he  made  it  with  a curtain  and  two  small 
flanks  parallel  to  those  of  the  enceinte ; in  others  it  con- 
sisted simply  of  two  wings  placed  on  the  prolongations  of 
the  faces ; and  finalfy,  he  gave  it  the  form  in  Fig.  2,  with  a 
small  curtain  and  two  wings,  wliich  is  the  one  at  present 
most  generallj'*"adopted.  The  relief  of  The  tenaille  is  so 
arranged  as  not  to  mask  the  fii^e  of  the  £anks  on  the  ditch 
of  the  enceintenslong  the  face$ ; for  this  purpose  Yauban 
places  its  interior  cresYon  a level  with'  the  site,  or  a little 
l)elow  it.  y V / ( ' 

The  ten^le^hffmair^^^  pi^erties;  it  covers  the 
postern  under  the  curtain ; masks  the  masonry  of  the  cur- 
tain and  flanks,  so  that  a breach  cannot  be  made  in  them, 
and  in  this  way  prevents  retrenchments,  resting  against 
those  parts,  from  being  turned ; place-of-arms  is  formed 
between  it  and  the  curtain,  where  troops  can  be  assembled 
for  sorties  in  the  ditches ; Anally,  its  Are  sweeps  the  ditch 
and  counterscarp,  and  helps  to  cover  the  retreat  of  troops 
from  the  other  outworks. 


48 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


70.  Main  Ditch.  Yaiiban  followed  no  invariable  rule' 
in  regulating  the  dimensions  of  the  enceinte  ditch  ; its  most 
usual  width  at  the  salients  of  the  bastions,  where  the  coun- 
terscarp is  an  arc  of  a circle,  is  about  3b  yards ; the  rest  of 
the  counterscarp  is  tangent  to  this  arc,  and  directed  upon 
the  opposite  shoulder  angles. 

71.  Demi-lune  and  Reduit.  Yauban  increased  the  ^ 
dimensions  of  the  demi-lune,  which  had  been  used  previous 
to  his  time. 

The  object  of  this  work  is  to  secure  the  gates  of  the  place 
from  a surprise ; to  mask  from  the  enemy’s  batteries  tlie 
hanks  and  curtain  of  the  enceinte ; to  give  cross-fires  on  the 
salients  of  the  bastions,  and  to  favor  sorties. 

The  plan  and  dimensions  of  the  demi-lune  vary  also  in 
Yauban’s  works.  Its  magistral  is  generally  laid  out  by 
taking  a point  on  the  bastion  face  at  10  yards  from  the 
shoulder  angle,  and  drawing  a line  from  this  point  to  the 
perpendicular  of  the  front,  so  as  to  make  the  face  of  the 
demi-lune  equal  to  of  the  exterior  side.  The  parapet  of 
the  demi-lune  is  the  same  as  that  of  the  enceinte;  its  com- 
mand is  3 feet  less  than  that  of  the  enceinte. 

All  the  outworks  in  this  system  are  commanded  by  the 
enceinte ; the  outworks  most  advanced  being  also  com- 
manded by  those  in  rear. 

The  ditch  of  the  demi-lune  is  generally  about  M yards 
wide  and  of  the  same  depth  as  that  of  the  enceinte  ; its 
counterscarp  and  that  of  the  enceinte  forming  a continuous 
wall. 

72.  To  strengthen  the  demi-lune,  and  secure  for  the 
troops  entrusted  with  its  defence  a safe  retreat  when  it  is 
carried,  Yauban  placed  in  it  a small  redoubt.  This  work,  in 
some  instances,  was  only  a simple  loop-holed  wall  with  a 
ditch  in  front ; sometimes  it  was  made  of  earth,  and  after 
the  commencement  of  the  siege. 

73.  Covered- way.  The  covered-way  envelopes  the  en- 
tire counterscarp.  The  general  width  of  the  covered-way 
is  12  yards. 

To  set  out  the  reentering  place-of-arms.  two  points  are 
taken,  at  20  yards  from  the  reentering  angle,  made  by  the 
interior  crests  of  the  covered-ways  of  the  demi-lune  and 
bastion,  and  upon  these  crests,  and  from  these  points  as 
centres,  with  radii  of  24  yards,  arcs  are  described  ; the  point 
of  their  intersection  being  joined  with  the  centres  gives  the 
crests  of  the  reentering  place-of-arms. 

The  parapet  of  the  covered  way  is  terminated  in  a glacis. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


49 


the  foot  of  which  is  from  40  to  50  ya^ds  from  the  interior 
crests. 

74.  Traverses.  To  close  the  pWces-of-arms,  and  enable 

the  troops  to  defend  the  covered-waj|foot  by  foot,  traverses 
of  earth  formed  into  parapets  are  placed  at  the  places-of- 
arms.  Defiles  or  passages  of  4 fe4t  are  left  between  the 
traverses  and  the  crest  of  the  covereji-way,  for  the  circula- 
tion of  the  troops.  The  coyered-waj^  is  palisaded  to  prevent 
surprise.  / 

Yauban  placed  a high  value  on  |his  work,  which,  to  use 
his  own  words,  “costs  less  to  the  defence  and  more  to  the 
assault  than  any  other  work.”  \ T|ie  covered-way  prevents 
all  access  to  the  ditch,  by  a strofig  ;’fire  of  musketry,  which 
sweeps  all  the  exterior  ground  ; it  Is  a secure  position  where 
troops  can  be  assembled  in  safety  for  sorties ; it  covers  the 
retreat  of  troops  from  the  exteriofi  into  the  other  works. 

75.  Communications.  In  ^^anl)an’s  front,  ramps  are 
made  to  ascend  from  the  plane  of' site  to  the  terre-plein. 

A posteftm,4^'  maderiinder  the  curtain  to  communicate  from 
the  intefiojr  tvjjth  the  ditclr;  another  postern  is  made  under 
the  tenaillp  fo  lead  to-thedemi-lune.  A double  caponniere^ 
which  is.a^pWaiige  covered  on  ei^ch  side  by  a parapet  termi- 
nated in  a glacis  towards  the  ditch,  covers  the  communica- 
tion through  the  ditch  to  tl^  gorge  of  the  demi-lnne. 
Single  caponnieres  are  placed  ifi  the  ditch  of  t.ie  demi-lune, 
and  cover  the  troops  from  tl^e  enemy’s  fire  through  its 
ditch.  I 

Stairs  are  placed  at  the  gorges  of  the  tenaille  and  demi. 
lune.  and  along  the  counterscarp  at  the  places-of-arms,  to 
ascend  from  the  ditch  to  the  t^re-pleins  of  those  works. 

To  communicate  with  the  exterior,  narrow  openings  are 
made  in  the  faces  of  the  redntering  place-of-arms,  to  lead 
from  the  terre-plein  to  the  glacis ; they  are  termed  sortie- 
passages  or  sally-ports  and  aie  closed  by  barriers. 

76.  Analysis.  In  the  trah  adopted  by  Yauban  for  the 

enceinte,  it  may  be  observed  tV  ' 

of  the  lines  of  the  front,  resnltl 
fensive  relations  both  for  the  ci 
day.  I 

1.  The  foot  of  the  scarp,  thrl 

curtain  and  the  bastions,  is  thoro^ 
the  Hanks.  i 

2.  The  length  of  the  flank 
many  cannon  at  least  as  the  assailant  can  place  to  counter- 
batter the  flank  from  the  glacis  crest  opposite  the  flank  ; and 


lat  the  length  and  positions 
ig  from  it,  are  in  good  de- 
mon and  small-arms  of  its 

nighout  the  length  of  the 
Ighly  swept  by  the  fire  of 

sufficient  to  contain  as 


50 


ELEMENTS  OE  PERMANEN;T  EORTIFICATION. 

the  flank  can  also  bring  an  efiScient  fire  of  small-arms  to 
bear  on  this  battery  of  the  assailant. 

3.  The  bastions  are  capacious,  and  would  admit  of  effi- 
cient interior  retrenchments  being  thrown  up  in  them, 
although  Yauban  does  not  indicate  this  auxiliary  in  his  first 
method. 

4.  The  tenaille  was  devised  mainly  to  mask  the  scarp  wall 
of  the  curtain  and  flanks,  whilst  its  relief  was  so  regulated 
as  not  to  intercept  the  fire;  of  the  flanks  on  the  enceinte 
ditch  before  the  bastioned  fpices. 

The  plan  of  the  earlier  t^nailles  consisted  of  two  flanks 
connected  by  a curtain,  which  were  parallel  to  the  same  lines 
of  tlie  enceinte.  This  fofm  was  subsequently  abandoned, 
as  the  flanks  were  found  t^  be  exposed  to  both  an  enfilading 
and  reverse  fire,  from  tfle  assailant’s  positions  in  front  of 
the  enceinte;  and  the  one  now  in  most  general  use, consist- 
ing of  either  two  wings  simply,  or  of  two  wings  connected 
by  a short  curtain,  adopted  in  its  place. 

The  tenaille,  however;  only  partially  subserves  its  object, 
as  it  does  not  cover  thejentire  height  of  the  scarp  of  the  en- 
ceinte curtain  and  flanks ; and,  what  is  a more  serious  de- 
fect, it  leaves  the  entir#  height  of  scarp  of  that  portion  of 
the  curtain,  opposite  |o  the  ditch  between  the  tenaille  and 
the  bastion  flank,  enti|ely  exposed,  from  the  same  position, 
and  liable  to  be  breacl|ed. 

5.  From  the  small|  size  of  the  derai-lune,  it  gives  but 
little  cov^er  to  any  portion  of  the  enceinte  scarp  except  the 
cnrtnn.  It  is  not  suficiently  thrown  to  the  front  to  give  a 
good  volume  of  croi-fire  on  the  glacis  in  advance  of  the 
bastion  salients  ; and|the  reentering  formed  at  this  point,  by 
the  two  adjacent  dfemi-lunes,  is,  from  the  same  cause, 
shallow  and  of  but  liitle  strength.  Owing  to  this  last  de- 
fect the  assailant  cap  easily  breach  and  storm  the  enceinte 
at  the  same  time  as  |he  demi-lune. 

Besides  these  defects  the  demi-lune  is  not  provided  with 
a permanent  reduit^  a work  necessary  to  enable  the  demi- 
lune to  make  a vigorous  defence,  by  the  support  it  affords 
the  assailed. 

().  From  the  width  given  to  the  demi-lune  ditch,  the 
covered-ways  are  exposed  to  a slant  reverse  fire,  from  which 
they  are  but  badly  screened  by  the  traverses.  Their  com- 
mand over  the  site  is  rather  too  little.  Their  main  defect, 
however,  is  the  small  size  given  to  the  reentering  place-of- 
arms.  and  the  failure  to  secure  this  important  position  for 
assembling  troops  for  sorties  by  a permanent  red  nit,  by 
which  any  open  attack  of  the  covered-way  could  be  checked. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


51 


7.  The  dimensions  given  both  to  the  enceinte  and  demi- 
lune ditches  present  a formidable  obstacle  to  an  open  as- 
sault, and  render  the  assailant’s  passage  of  the  ditch  by  the 
sap  also  more  difficult.  The  derni-lune  ditch,  however,  offers 
a wide  opening  through  which  the  scarp  of  the  bastioTi-face 
can  be  seen  down  to  its  foot  from  the  assailant’s  batteries 
on  the  glacis  crest  in  the  prolongation  of  the  demi-lune  ditch. 

8.  The  communications  within  the  enceinte,  and  from  it 
to  the  main  ditch,  are  sufficient  and  convenient  for  the  char- 
acter of  the  defence  designed.  Those  of  the  outworks  are 
for  the  most  part  narro\^,  inconvenient,  and  but  badly 
screened  from  the  assailant’s  fire,  and  therefore  do  not  furnish 
a good  provision  for  an  active  defence  beyond  the  enceinte. 

9.  The  great  command;  over  the  site,  and  the  high  relief 
given  to  the  enceinte,  ard  very  much  in  favor  of  the  defence 
both  as  to  the  effect  of  tjhe  fire  on  the  assailant's  approaches 
and  for  security  against  fin  escalade.  But  in  attaining  these 
objects  Vauban  has  left  exposed  to  the  assailant’s  distant 
fire  a considerable  po4;ion  of  the  scarp  wall,  which,  being 
destroyed,  would  lay  tfte  enceinte  open  to  a surprise. 


77.  Cormontaignp,  born  1696,  died  1752,  the  immediate 
successor  of  Yaubail!,  holds  a place  only  second  to  this  mas- 
ter of  the  art  in  me  estimation  of  the  engineers  of  the 
French  school.  0ormontaigne,  who,  to  superior  abilities 
united  a wide  rangi^  of  experience  both  in  the  construction 
and  in  the  attack of  permanent  works,  studied  with  great 
care  the  results  of  jYau ban’s  immense  labors.  In  planning 
the  front  which  h^s  received  his  name.  Cormontaigne  seems 
to  have  applied  hijnself  rather  to  remedy  the  defects  notice- 
able in  the  methods  of  Yauban,  than  to  produce  any  radical 
change  in  the  combinations  which  had  thus  far  received  the 
sanction  of  engineers  generally.  He  was  thus  led  to  reject 
the  2d  and  3d  ifiethods  of  Yauban,  and  to  take  the  first 
method  as  the  ba^is  of  his  own  changes. 

78.  Cormontajgne  was  the  first  to  develop  clearly  the 
influence  of  large  demi-lunes  on  the  progress  of  the  attack, 
by  their  forming  deep  reenterings  between  them  in  front  of 
the  bastion  salients ; and  also  the  increased  strength  gained 
by  fortifying  on  a right  line,  or  on  polygons  with  a great 
number  of  sides,  as  in  both  of  these  cases  the  fronts  assailed 


COI^^MONTAIGNE  S METHOD, 


UNIVtRiJITY  OF  ILLiNO/S 
LIBRAfi)C  ■ 


52 


ELE^klENTS  OF  PERMANENT  FORTIFICATION. 


principle  that  no  masonry 
Jjatteries  of  the  assailant^ 
arranged  the  height  of  his 


tking  froin  view  the  entire 
glacis,  from  all  positions  in 

and  profile  of  Yauban’s  1st 
ibove  as  a basis, 
cations  of  Yan 
e various  works  of  Cormon- 
in  his  memoirs  as 


cannot  be  enveloped  bj  the  assailaiit’s  works,  and  the  demi 
lunes  from  their  salient  position  intercept  the  prolongations 
of  the  bastion-faces,  and  thus  mask  them  from  the  positions 
from  which  alone  an  enfilading  fifre  could  be  brought  upon 
them. 

79.  He  likewise  lays  down  as 
should  he  exposed  to  the  distan 
and  to  obtain  this  point  he  has  s 

principal  scarps,  and  the  commlnd  given  to  the  glacis  crest 
in  front  of  them,  that  the  top  of  the  scarp  shall  not  lie  above 
the  level  of  the  crest,  thus  m ' 
scarp,  by  the  earth  forming  th 
advance  of  the  glacis  crest. 

His  modifications  of  the  pla 
method  chiefly  result  from  the 

80.  Enceinte.  The  modiScations  of  Yauban’s  trace 
(Fig.  4,  PI.  10)  are  different  in  t 
taigne ; but  the  following  he  |ndicates 
the  one  preferred  by  him. 

The  exterior  side  is  360  yards ; the  perpendicular  the 
faces  of  the  bastions  of  the  exterior  side  ; the  fianks  are  40 
yards,  and  are  so  placed  that  the  curtain  shall  be  120  yards. 
This  combination  makes  the  lines  of  defence  somewhat  less, 
and  the  bastions  larger  than  in  Yauban’s  method. 

• The  dimensions  of  the  enceinte  ditch  are  so  regulated  by 
Cormontaigne  as  to  furnish  earth  sufiicient  for  the  embank 
ments.  It  is  28  yards  wide  at  the  salient  and  from  2 to  4 
yards  wider  opposite  the  tenaille;  this  admits  the  entire  fire 
of  the  flanks  to  sweep  the  ditch. 

81.  Tenaille.  The  tenaille  is  made  with  a curtain  and 

wings ; a ditch  10  yards  wide  being  left  between  it,  the  cur- 
tain, and  the  flanks.  * 

82.  Demi-lune.  Cormontaigne  placed  little  value  on 

small  demi-lunes,  as  they  form  but  slight  and  therefore  weak 
reenterings  before  the  bastions,  and  consequentl  y retard  but 
little  the  enemy’s  attack  upon  them ; besides  t|is,  a small 
demi  lune  covers  but  very  imperfectly  the  shoulder  angles 
of  the  bastions.  I 

To  remedy  these  defects,  his  demi-lune  is  so  Inid  out  that 
the  prolongations  of  the  magistrals  of  its  faces  will  intersect 
the  bastion-faces  at  30  yards  from  the  shoulder  angles ; the 
lengths  of  its  faces  being  120  yards. 

The  ditch  of  the  demi-lune  is  20  yards  wide;  its  depth  is 
the  same  as  that  of  the  enceinte.  By  thus  enlarging  the 
demi-lune,  sufficient  space  is  gained  to  place  a strong  reduit 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


in  its  interior.  The  defence  of  the  demi-lune  may  be  made 
with  more  obstinacy  from  the  support  it  receives  from  the 
rednit ; and  the  enemy  will  be  obliged  to  carry  it  before  he 
can  assault  the  breach  he  may  have  made  in  the  bastion 
face,  as  this  breach  is  seen  in  reverse  by  the  fire  of  the  flanks 
of  this  work. 

\ 83.  Demi-lune  Reduit.  To  circumscribe  as  much  as 
practicable  the  space  in  the  demi-lune  which  the  enemy, 
after  he  gains  it,  requires  for  his  works,  the  extremity  of 
the  demi-lune  terre-plein,  which  is  also  the  top  of  the  couuter- 
iscarp  of  the  reduit,  is  drawn  at  20  yards  from  the  magistral 
of  the  face ; the  ditch  of  the  reduit  is  10  yards  wide,  and 
the  magistral  of  its  face  is  parallel  with  the  counterscarp. 
By  this  arrangement  the  ditch  is  well  flanked  by  the  face 
of  the  bastion  near  the  shoulder  angle. 

To  lay  out  its  flanks,  the  counterscarps  of  the  enceinte  are 
prolonged  to  intersect  the  perpendicular  of  the  front ; from 
this  point  of  intersection  a distance  of  20  yards  is  set  ofl: 
■along  each  counterscarp ; the  two  points  thus  obtained  are 
joined  by  a right  line,  which  is  the  gorge  of  the  work : 
from  the  extremities  of  the  gorge  two  lines  are  drawn  paral- 
lel to  the  capital  of  the  demi-lune,  these  lines  limit  the  terre- 
plein  of  the  flanks ; the  magistrals  of  the  flanks  are  drawn 
parallel  to  and  at  16  yards  fToin  the  last  lines. 

84.  Covered-way,  etc.  The  general  width  of  the 
covered-way  is  10  yards.  Cormontaigne  enlarged  consider- 
ably the  reentering  place-of-arms,  to  which  he  added  a 
reduit  with  a revetted  scarp  and  counterscarp.  The  addi- 
tion of  this  work  is  a great  improvement  upon  the  covered- 
way of  Yauban,  who  indicates  in  his  works  small  reduits  of 
earth,  or  tambours  of  wood,  for  the  same  purpose. 

Cormontaigne’s  reduit  increases  the  strength  of  the 
covered  way ; the  troops  assembled  in  the  covered-way  for 
•sorties  are  secure  under  its  fire ; it  sees  in  reverse,  and  pro- 
tects any  breach  made  in  the  face  of  the  demi-lune;  finally, 
it  serves,  in  connection  with  the  extremity  of  the  demi-lune, 
to  cover  the  opening  left  between  the  flanks  of  the  bastion 
and  the  wings  of  the  tenaille,  through  which,  if  a breach 
was  made  in  the  curtain,  the  interior  retrenchments,  resting 
upon  either  the  flank,  or  faces  of  the  bastion,  could  be 
turned. 

To  lay  out  the  interior  crests  of  the  reentering  place-of- 
arms,  two  points  are  taken  on  the  counterscarps  of  the  bas- 
tion and  demi-lune  at  54  yards  from  their  point  of  intersec- 
tion ; from  these  points'  as  centres,  with  radii  of  60  yards, 


54 


ELEMENTS  OF  PEKMANENT  FORTIFICATION. 


arcs  are  described,  whose  intersection  joined  with  the  cen- 
tres gives  the  direction  of  the  faces. 

The  magistral  of  its  rediiit  is  found  by  a similar  construc- 
tion ; distances  of  40  yards  being  set  off  along  the  counter- 
scarps, and  the  faces  being  drawn  from  these  points  so  as 
to  be  36  yards  long.  The  ditch  of  the  reduit  is  5 yards 
wide  and  yards  deep. 

Traverses  are  placed  along  the  covered-way,  to  close  the 
places-of-arms,  defend  the  covered-way,  and  intercept  pro- 
jectiles tired  in  ricochet. 

The  crest  of  the  glacis  is  broken  into  acremaillere  line  to 
allow  room  for  the  defiles  of  the  traverses.  The  short 
branches  of  the  cremaillere  throw  a tire  on  the  salients  of 
the  covered-way  ; the  positions  of  the  long  branches  are  so 
taken  that  the  defiles  may  be  seen  and  swept  by  the  fire  of 
the  works  in  their  rear. 

85.  Profiles.  Cormontaigne,  after  a series  of  trials, 
whose  object  was  to  give  the  ditches  such  dimensions  that 
they  should  furnish  the  earth  required  for  the  embank- 
ments, regulated  the  command  of  the  different  works  as 
follows : 

The  lowest  work,  which  is  the  demi-lune  covered-way,  he 
lays  down  as  a rule,  shall  command  the  exterior  ground  by 
not  less  than  feet ; and  the  works  most  advanced  shall 
be  commanded  by  those  in  the  rear. 

It  was  found  that,  for  the  purpose  of  equalizing  the  ex- 
cavations and  embankments  of  the  front,  the  crest  of  the 
demi-lune  covered- way  should  have  a command  of  10^  feet 
above  the  natural  ground. 

The  crest  of  the  bastion  covered-way  and  of  the  reenter- 
ing place-of-arms  commands  the  crest  of  the  demi-lune 
covered-way  by  2 feet. 

The  magistral  of  the  enceinte  is  horizontal,  its  elevation 
being  the  same  as  the  mean  elevation  of  the  crest  of  the 
bastion  covered-way. 

The  scarp  wall  is  30  feet  high.  This  dimension  has  until 
recently  been  generally  adopted  by  engineers,  a wall  of  this 
height  opposing  a sufficient  obstacle  to  an  attempt  at  esca- 
lade. 

The  salient  of  the  bastion  commands  its  covered-way 
by  8 feet.  The  absolute  relief  of  the  flanks  is  38|-  feet. 
With  this  relief  a piece,  firing  under  a depression  of  ^ 
through  an  embrasure  in  the  flank,  and  in  the  direction  of 
the  curtain,  will  strike  the  bottom  of  the  ditch  at  the 


ELEMENTS  OF  PERMAJ^ENT  FORTIFICATION. 


55 


middle  point  of  the  curtain ; so  that  were  the  relief  in- 
creased, the  length  of  curtain  remaining  the  same,  the  ditch 
would  no  longer  be  thoroughly  tianked. 

The  relief  of  the  tenaille  is  determined  as  in  Yauban’s 
method,  so  as  not  to  mask  the  fire  of  the  flanks  upon  the 
ditch  opposite  the  extremity  of  the  derni-lune ; as  it  is  here 
that  a breach  may  be  made  in  the  bastion  face,  through  the 
ditch  of  the  demi-lune. 

The  demi-lune  is  commanded  by  the  enceinte  3 feet,  and 
l)y  its  own  reduit  feet.  The  demi  lune,  therefore,  com- 
mands its  covered-way  7- feet,  which  is  more  than  is  indis- 
pensably requisite;  for  an  enemy  standing  on  the  crest  of 
the  covered-way  cannot  have  a plunging  fire  into  a work 
in  the  rear  of  it,  if  the;  latter  commands  its  crest  by  5 
feet. 

The  reduit  of  the  reentering  place  of-arms  commands  the 
crest  of  the  glacis  only  4^  feet;  its  interior  crest  is  so  placed, 
as  not  to  mask  the  fire  of  the  bastion  faces  on  the  glacis  in 
advance  of  it. 

The  interior  crests  of  all  the  works  are  7|-  feet  above  their 
terre-pleins,  except  that  of  the  tenaille,  which  is  6|-  feet ; 
and  of  the  reduit  of  the  reentering-place-of-arms,  which  is  9 
feet. 

The  interior  crests  of  the  faces  of  all  the  works  exposed 
to  enfilading  fires  are  one  foot  higher  at  the  salients  than  at 
the  extremities. 

The  profile  of  the  parapet  of  the  principal  outworks  is  the  ' 
same  as  that  of  the  enceinte. 

86.  Communications.  The  communications  are  gen- 
erallyof  the  same  nature,  and  placed  about  in  the  same  posi- 
tions as  in  Yauban’s  method. 

87.  Glacis,  The  planes  of  the  glacis  are  so  determined 
that  they  may  be  swept  by  the  fire  of  the  works  in  the  rear ; 
their  inclination  is  usually  about  twenty-four  base  to  one 
altitude. 

Interior  Retrenchments.  Cormontaigne  indicates  the 
gorge  and  shoulders  of  the  bastion  as  the  position  for  an  in- 
terior retrenchment,  when  this  addition  to  the  front  is  made 
solely  with  a view  of  disputing  the  breach  in  the  bastion 
and  its  interior  witli  the  assailant.  In  this  case  he  gives  the 
retrenchment  the  form  of  a tenaille,  or  a bastioned  front, 
resting  it  either  upon  the  shoulder  angles  of  the  bastion,  or 
upon  the  two  adjacent  curtains  on  the  points  beyond  the 
prolongation  of  the  ditch  between  the  tenailles  and  the 


50  ELEMENTS  OF  PERMANENT  FORTIFICATION. 

flanks,  and  in  this  position  he  gives  it  the  fc^rm  of  a bas- 
tioned  front.  / 

In  the  former  case,  the  portion  of  the  interior  of  the  bas- 
tions between  the  flanks  is  preserved  for  ^iie  defence,  but 
the  retrenchment  is  liable  to  be  turned,  by  a breach  made 
in  the  flank,  or  in  the  portion  of  the  curt^*n  where  it  joins 
the  flank.  In  the  latter  case  a breach  in  the  bastion  places 
the  whole  of  the  interior  within  view  of  the  assailant,  but 
the  retrenchment  itself  is  secure,  from  its  position,  from 
being  turned,  as  a breach  in  the  curtain  cannot  be  made  in 
rear  of  it. 

88.  Cavalier.  When  a greater  command  of  the  site 

than  that  afforded  by  the  enceinte  is  requisite  on  any  front, 
Cormontaigne  places  a cavalier  within  the  bastion.  To  this 
work  he  gives  the  same  form  as  that  of  the  bastion  ; placing 
the  faces  and  flanks  of  the  two  parallel  to  each  other.  The 
faces  of  the  cavalier  are  alone  revetted,  as  well  as  the  counter- 
scarp of  their  ditch,  which  is  cut  within  the  bastion.  This 
ditch  is  broken  off  at  the  shoulder  angles  of  the  cavalier,  and 
directed  upon  the  faces  ; these  portions  also  having  a revetted 
scarp  and  counterscarp.  A parapet  is  thrown  up  behind 
the  scarp  and  between  the  flank  of  the  cavalier  and  the 
bastion  faces ; thus  isolating  the  anterior  portion  of  the  bas- 
tion, and  furnishing  an  interior  retrenchment  which,  when 
the  shoulders  and  flanks  of  the  bastions  are  masked  from  the 
assailant’s  view,  can  only  be  carried  by  a breach  made  either 
in  the  cavalier  face,  or  in  the  portions  resting  on  the  cavalier 
and  bastion  faces.  . 

89.  Analysis.  From  the  preceding  description,  it  ap- 
pears that  the  most  important  mollifications  made  by  Cor- 
montaigne in  Yauban’s  first  metho(  , consist: 

1.  In  the  means  taken  to  covert!  e masoiiry  irom.  distant 
batteries. 

2.  In  more  capacious  bastions  msceptible  of  receiving 
efficient  permanent  interior  retrencl  ments. 

3.  In  an  enlarged  demi-lune,  whidi  places  the  bastions  in 
strong  reenterings,  covers  the  shoulder  angles,  and  admits 
of  a reduit  in  its  interior,  which  wo  k strengthens  the  demi- 
lune, and  sees  in  reverse  the  brea  di  made  in  the  bastion 
face. 

4.  In  an  enlarged  reentering  pla  3e-of-arms,  containing  a 
reduit  which  strengthens  the  entire  covered-way,  and  covers 
the  movement  of  the  troops  in  sorri3S. 

These  modifications,  although  o great  value,  and  con- 
stituting an  important  step  in  the  ait,  still  leave  much  to  be 


ELEMENTS  OE  PERi^NENT  FORTIEICATION. 
'i 


57 


■desired  ; and  engineers  sn 
.sought  to  remedy  the  defc 
following  are  the  principal] 
1.  The  enceinte  has  rati 


ice 
its  of 


Cormontaigne’s 


his  method, 


time  have 
of  which  the 


too  slight  a command,  and  is 


without  any  bomb-proof  shelters. 

2.  The  inclination  of  mie  superior  slope  of  its  parapet, 
which  is  is  too  small  tofiave  the  ditches  well  flanked. 

3.  A breach  can  be  mafe  in  the  bastion  face  through  the 
ditch  of  the  demi-lune. 

4.  There  are  dead  spa^s  in  the  ditch  of  the  demi-lune, 
near  the  extremities  of  it^faces. 

5.  The  reduit  of  the  re|ntering  place-of-arms  is  not  tena- 
ble after  the  demi-lune  istaken. 

6.  The  traverses  of  theicovered-way  do  not  afford  the  re- 
quisite protection  to  that  Iv  ork. 

7.  Finally,  the  commuiications  are  mostly  inconvenient, 
.and  not  well  covered  froil  the  assailant’s  fires. 


90.  Counterguard. 

his  enceinte  with  a high 
and  form  as  in  his  first 
ing  arrangements  for  thei 
■of  masonrv,  which  are 


anban,in  his  third  method, forms 
?arp  wall,  of  the  same  dimensions 
ffhod ; and  he  procures  his  flank- 
mceinte  by  small  bastioned  towers 
ise mated  in  the  lower  story,  and 
have  an  open  battery  in  |he  upper,  covered  by  a masonry 
parapet.  I 

This  enceinte  he  covels  with  spacious  counte-rgiiards  of 
the  form  of  lunettes;  thrffaces,  flanks,  and  gorges  of  which 
are  revetted,  and  wFich  cclver  the  bastioned  towers  of  the  en- 
ceinte; and  between  the  tanks  of  these  counterguards,  and 
covering  the  curtain  of  tlife  enceinte  between  the  bastioned 
towers,  he  places  a tenaill|. 

A demi-lune,  in  the  fori  of  a lunette,  is  placed  in  front 
of  the  counterguards  an|  tenaille ; within  which  he  has 
placed  a reduit  with  a revetted  scarp  and  counterscarp.  The 
whole  of  this  combinatioif  of  outworks  he  incloses  wflth  a 
■cov'ered-way  arranged  in  the  usual  manner. 

91.  Cormontaigne  usesf  the  counterguard  only  as  an  ex- 
ceptional outwork  ; and  h^s  applied  it,  in  some  of  the  works 
constructed  by  him,  to  strengthen  a point  that  would  other- 
WTse  have  been  too  weak*;  but  not  like  Vauban,  as  a con- 
stituent part  of  his  methoq. 

92.  Two  of  the  most  eminent  modern  .engineers,  Coe- 
hoorn,  born  1641,  died  1T|)4,  and  Carnot,  born  1753,  died 
1823,  in  their  methods^  us^  earthen  counterguards  to  cover 
their  enceintes,  giving  them  only  sufficient  thickness  at  the 
fop  for  a parapet  and  a banjquette  for  infantry  ; so  that,  be- 


58 


ELEMENTS  OF  PEEMANENT/ FORTIFICATION. 


ing  taken  by  the  assailant,  he  will/  not  find  snfi&cient  roonr 
to  place  a breaching  battery  upon  their  terre  pleins  against 
the  enceinte.  In  this  way  they  /serve  chiefiy  as  masks  or 
face  covers  to  the  enceinte  faces.  / 

93.  Haxo,  born  1774,  died  1$38,  forms  of  the  counter- 
guard a constituent  element  of  fhis  method,  giving  it,  like- 
Van  ban,  the  form  of  a lunette.  | 

94.  Noizet,  born  1792,  died  1885,  although  adopting  the 
features  of  Cormontaigne’s  method  as  the  basis  of  his,  speaks 
of  the  counterguard  as  a valuable,  and  sometimes  a neces- 
sary, element  of  a front ; prefdrring  it  in  some  cases  to  the- 
demi-lune. 

Like  all  other  outworks,  wh  m used,  it  should  be  flanked 
by  the  enceinte  flanks ; be  swe  pt  on  the  interior  by  the  fire 
of  its  faces ; and  not  intercept  their  fire  on  the  ground, 
in  advance  of  it.  1 


4 


METHODS  OF  THE  SCHOOLS!  OF  MEZIEEES  AND  METZ. 


95.  The  schools  of  application  for  engineer  and  artillery 

officers,  first  established  at  Mezieres  and  subsequently  at 
Metz,  now  at  Fontainebleau,  ha|s  given  to  France,  from  about 
the  period  of  the  French  Rek^olution  down  to  the  present 
day,  the  far  greater  portion  of  the  many  able  officers  who 
have  gained  such  universal  an(|  deserved  celebrity  for  these 
two  corps.  5 

In  these  schools  the  precepts  of  Yauban  and  Cormon- 
taigne  have  been  jealously  regarded  as  the  highest  authority, 
and  their  manuscripts  and  published  works  have  formed  the 
basis  of  the  instruction  given  ip  them. 

96.  Some  slight  modifications  were  proposed  in  the  front 
of  Connontaigne  by  two  engineers,  Chatillon  and  Duvi- 
gneau^  2.\\^  taught  by  them  in  the  course  of  permanent  for- 
tification given  in  the  school.  i These  changes  chiefly  con- 
sisted in  enlarging  the  demi-pune  and  making  it  more 
salient;  and  in  placing  in  the  flanks  of  its  reduit  casemates 
for  cannon  with  reverse  views  on  the  breaches  that  might 
be  made  in  the  bastion  faces. 

97.  The  teaching  of  the  school  of  Metz  received  its  prin- 
cipal impress  from  General  Noizet,  himself  a pupil  of  Gen- 
eral Haxo,  regarded  as  the  first  among  the  successors  of 
Yauban  and  Cormontaigne,  who  for  several  years,  while  a. 


/ 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


59 


eaptriiii  of  engineers,  performed  fche  functions  of  professor 
of  fortification,  and  wlio  subseqiientlj  gave  to  the  public 
the  results  of  his  lectures  delivered  in  the  school. 

98.  The  front  which,  until  si  few  years  back,  has  been 
taught  in  this  school,  goes  by  fche  appellation  of  Noize€s 
Method.  In  it  there  is  no  sensible  departure  from  the 
views  and  methods  of  Vauban  fend  Cormontaigne ; the  ob- 
ject being  to  introduce  such  modifications  into  the  front  of 
the  latter  as  would  remedy  sope  of  its  acknowledged  de- 
fects. 

In  doing  this,  another  objecl  was  kept  in  view  which  was 
to  present,  in  the  combinations  of  this  front,  a problem,  in 
the  solution  of  which  the  pupil  would  be  called  upon  to  ap- 
ply both  the  elementary  principles  of  fortifications  and  the 
geometrical  methods  that  tlie  engineer  has  to  use  as  his 
principal  tool  in  such  probleiBS,  to  a special  case,  that  of  a 
front  adapted  to  a horizontalAsite.  It  was  in  this  point  of 
view  that  the  analysis  and  construction  of  this  front  were 
for  many  years  adopted  as  tl|e  basis  for  the  elementary  in- 
struction given  in  permanenti  fortification  in  this  Institution. 


NOIZET1S  METHOD. 

99.  General  Requirements.  Noizet  in  his  front  takes 
as  the  basis  of  the  construction  of  the  enceinte  the  length  of 
the  exterior  side,  and  the  cohimand,  assuming  these  within 
the  limits  laid  down  by  Yauban  and  Cormontaigne,  and  in 
the  combinations  of  outworks  with  the  enceinte,  following 
the  latter  engineer ; introducing  only  such  modifications  as 
seem  to  best  fulfil  the  general  conditions  of  the  problem. 

100.  General  data  of  the  Enceinte.  In  the  follow- 
ing description  of  the  front  of  Koizet,  (Plate  lla^  Fig.  1,) 
the  plane  of  comparison  is  assumed  at  60  feet  below  the 
horizontal  plane  of  site,  the  reference  of  which  will  be,  there 
fore,  (60.0).  The  yard  is  taken  as  the  unit  for  the  horizon- 
tal dimensions  of  the  plan  ; and  the  foot  as  the  unit  for  the 
references  and  vertical  dimensions. 

Converting  the  French  measures  into  their  equivalent 
English  units,  the  exterior  ^de  of  the  front  is  380  yards ; 
the  height  of  the  scarp  wall  ’33  feet ; the  command  of  the 
interioi-  crest  of  the  curtain  over  the  plane  of  site  21  feet;, 
and  its  height  above  the  magistral  13  feet. 


f 


60 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


The  dimensions  of  the  exterior  side  and  of  the  relief,  as 
here  given,  are  so  taken  as  to  secure  an  efficient  flankino* 
arrangement  of  the  curtain  ; and  of  the  outworks  by  the 
bastion  faces. 

101.  Profile  of  Enceinte.  The  profile  of  the  en- 
ceinte here  given  is  similar  to  that  of  Cormontaigne,  and 
was  adopted  by  subsequent  'engineers  until  the  more  re- 
cently modified  one  already  described. 

Its  slopes  and  dimensions  are  as  follows: — The  scarp  and 
counterscarp  slopes  2_^or  one  base  to  twenty  altitude.  Ex- 
terior slopes  i or  45°.  Superior  slope  i.  Interior  slope  f. 
Banquette  slope  Earn part  slope  f.  Terre-pleins  8 feet 

below  the  interior  crests.  Berm  2 feet.  Distance  between 
the  magistral  and  foot  of  the  exterior  slope  1.5  feet.  Thick- 
ness of  parapet  20  feet.  Height  of  interior  crest  above  the 
banquette  tread  4.5  feet.  General  width  of  rerre-plein  esti- 
mated from  the  vertical  through  the  intenor  crest  48  feet. 

102.  Magistral  of  the  Curtain.  The  length  of  this 
IS  a minimum  consistent  with  the  artillery  fire  of  the  fianks 
passing  IJ  feet  above  the  bottom  of  the  ditch  at  the  centre; 
this  fixes  it  between  139  and  140  yards. 

103.  Magistral  of  the  Enceinte.  The  perpendicular 

to  the  front  is  i the  exterior  side,  the  lines  of  defence  are 
drawn  as  usual,  the  flanks  ma^e  an  angle  of  with  the  per- 
pendicular to  the  front ; the/  faces  are  determined  by  the 
curtain  and  flanks.  / 

A limited  amount  of  protefction  from  enfilade  is  given  to 
the  long  lines  by  giving  greater  command  to  the  bastion 
and  demi-lune  salients,  but  jthe  scarp  walls  are  not  corre- 
spondingly raised  j 

104.  The  Outworks.  tThese  satisfy  the  general  con- 
ditions of  defence,  and  are  [carefully  designed  "to  fulfil  the 
requirements  of  a problem  ii  fortification-drawing,  in  which 
the  details  are  thoroughly  "ylvorked  out,  and  the  determina- 
tion of  whose  relations  involve  most  of  the  geometrical 
problems  met  with  in  such  ^ork.  , 

105.  Remarks.  The  principal  points  of  diflference 
from  Cormontaigne’s  methpd  consist  in  a change  in  the 
directions  and  lengths  of  tjie  faces  of  the  redoubt  of  the 
reentering  place-of-arms.  without,  however,  destroying  its 
usefulness  in  connection  wirh  the  ravelin  as  a mask  to  the 
curtain  ; in  making  a cut  ovi^oujpure  in  the  ravelin  face  in 
front  of  the  redoubt  of  the  rbentering  place  of-arms,  to  pre- 
vent the  redoubt  being  turned  when  the  besiegers  get  pos- 
session of  the  ravelin ; in  prolonging  the  bastion  counter- 

t 


f 


ELEMENTS  PERMA/eXT  FORTIFICATION. 


61 


scarp  across  the  ditch  of  the  fleinid line  and  its  redoubt,  and 
constructing  in  the  tirst  a f^e-cover  for  the  bastion,  and  a 
covered  comnuinication  ani  single  caponier  for  sweeping 
the  ditch ; and  in  the  secoi^,  a mask  to  cover  the  shoulder 
angle  from  lire  coming  thipugh  the  redoubt  ditch;  and  in 
placing  four  traverses  in  the  demi-lune  covered-way,  which 
is  made  wider  toward  th|  reentering  place-of-arms  to  give 
better  cover  to  the  defiles/of  the  traverses. 

A complicated  system  pi  glacis  planes  was  designed,  add- 
ing to  the  value  of  the  f Ant  as  a problem  in  construction. 

106.  General  Remarks.  In  the  combination  and  ar- 
rangement of  the  outworks,  Noizet  has  followed  closely  the 
methods  of  CormontaigBe,  and  of  the  school  of  Mezieres. 
The  princi{)al  objections  to  these  combinations  are: 

1.  That  from  the  cornmand  given  to  these  works,  a con- 
siderable portion  of  thi  fire  of  the  enceinte,  on  the  site  ex- 
terior to  these  worksl  is  obstructed  by  them.  And  that 
some  of  these  works,  like  the  reduit  of  the  demi-lune.  and 
the  parapet  behind  thfe  cut  in  the  demi-lune  face,  mask  the 


interior  of  the  demi 
2.  That  from  the 
kind  of  communicat 
ditch,  sorties  on  the 
made  in  small  and  fe 


ne  from  a portion  of  this  fire, 
vetted  gorges  of  these  works,  and  the 
on  between  them  and  the  enceinte 
issailants’  wmrks  in  them,  can  only  be 
ble  parties. 

3.  That  the  traverses  of  the  covered-ways  obstruct  the 
free  movement  of  tix  ops  along  them,  and  also  obstruct  the 
lire  of  the  enceinte  o i their  terre-pleins. 

I.  The  plunging  fi  ^e  of  modern  artillery  searches  out  the 
masonry  scarps  over  he  glacis  and  through  the  ditches  of 
the  outworks,  makina  it  practicable  to  breach  the  enceinte 
by  the  distant  lire. 

107.  For  these  detects  various  changes  have  been  sug- 
gested, and  some  of  tliem  have  been  adopted  in  some  of  the 
more  recent  Europeari  fortifications. 

These  consist — 

1.  In  giving  a greater  command  to  the  enceinte  than  that 
usually  found  in  the  methods  described. 

2.  In  suppressing  tli4  reduit  of  the  demi-lune,  as  usually 
constructed,  in  decreasing  its  command,  and  replacing  it  by 
a casemated  reduit  plac^  at  the  gorge  of  the  demi-lune. 

3.  In  suppressing  tha  traverses  of  the  coyered-ways  ex- 
cept those  enclosing  the  weentering  place-of-arms  ; depend- 
ing on  the  short  brancheslof  the  cremailleres  into  which  the 
interior  crest  of  the  covered-way  is  broken  to  limit  the 
effects  of  enfilade  fire,  andun  reducing  its  width,  to  bring  its 


ELEMENTS  OF  PEKMANENT  /ORTIFICATION. 


'/ 


4.  To  replace  the  narrow  stai^  used  by  Yaiiban  for  com- 


mniiicating  with  the  terre-pleips  of  the  outworks,  by  wide 
ramps  to  facilitate  sorties  in  la|^ge  bodies. 

5.  To  hauk  both  the  cov,ered-way  and  the  demi-lune 
ditch  by  a casemated  reduit/placed  within  the  reentering 
place-of-arms. 

G.  To  make  the  communipatious  more  ample  and  direct. 

7.  To  simplify  the  outworks,  suppressing  some,  and  mak- 
ing the  others  more  subseiwient  to  the  artillery  fire  of  the 
enceinte.  / 

Most  of  these  modifications  have  been  introduced  into  the 
front  now  taught  at  the  school  of  Fontainebleau. 

Plate  1,  Figs.  4 and  6,  ^how  the  latest  and  simplest  form 
of  the  bastioned  system  \|-ithout  outworks. 

108.  In  every  coml  ation  the  engineer  must  be  guided 
by  the  exigencies  of  tl  sites  that  he  is  called  upon  to  for- 
tify, the  character  of  th  :lefence  that  it  is  proposed  that  the 
work  shall  make,  and  t relative  pecuniary  cost  of  differ- 
ent combinations.  In  king  tliis  last  consideration,  how- 
ever, into  account,  he  s uld  not  forget  that  the  pecuniary 
outlay  for  a work  that  11  protract  the  defence  only  a few 
days  longer  may  often  3ar  no  comparison  to  the  benefits 
arising  from  it. 

Note. — A full  descriptio  )f  Noizet’s  method,  with  the  analysis  of 
the  different  parts,  will  be  f ad  in  the  unrevised  edition  of  this  work. 


109.  Choumara,  boRn  1787,  died  1870,  a French  officer  of 
engineers,  of  distinguished  abilities,  is  the  author  of  several 
remarkable  memoirs  op  the  defects  of  the  bastioned  system, 
and  the  means  by  which  they  may  be  removed  and  much  ad- 
ditional strength  be  thereby  given  to  the  defences.  His 


1.  That  part  of  a perfnanent  work  which  can  undergo  no 
modification  during  th^  progress  of  a siege  is  the  masonry, 
and  it  may  therefore  be  regarded  as  the  really  permanent 
feature  ; all  the  parts  of  earth,  as  the  parapets,  etc.,  being 
susceptible  of  such  mo4ifications  as  circumstances  may  de- 
mand. 


YI. 


CHotlMAEA’s  METHOD. 


propositions  for  this  ;^urpose  may  be  briefiy  stated  as  fol- 
lows : ) 


ELEMENTS  OF  PERMANENT 


'ORTIFICATION. 


63 


This  Choumara  terms  the  indeiendence  of  the  paravets 
:as  respects  the  scarps.  1 

The  latter,  upon  which  the  security  of  the  work  against 
an  open  assault  or  a surprise  df pends,  must  necessarily  re- 
ceive a direction,  such  that  it  (An  be  swept  by  the  hanking 
arrangements,  a necessity  that  floes  not  exist  for  the  para- 
pets, which  may  receive  any  (Erection  compatible  with  the 
interior  space.  / 

The  parapets  may  thereto®  be  thrown  back  from  the 
salients,  as  in  the  bastion,  12,  Fig.  1,)  and  receive  a 
curvilinear  form  to  throw  a treater  volume  of  fire  in  the 
direction  of  the  capital.  | 

Or  they  can  be  retired  fr|)in  the  faces,  as  in  the  bastion 
(Fig.  a),  for  the  purpose  cat  giving  them  such  directions 
that  their  prolongations  shall  cut  the  adjacent  demi-lunes, 
and  thus  be  masked  from  ejifilading  views. 

Or  they  may  be  prolon^d  so  as  to  afford  a greater  col- 
umn of  flank  lire,  as  in  thf  flanks*!,  (Fig.  1,)  or  they  may 
be  broken  into  any  direction  for  the  same  purpose,  or  to 
give  a more  effective  direction  to  their  Are. 

Or,  Anally,  they  may  l|e  thrown  back  from  the  scarp 
walls  instead  of  resting  iipmediately  upon  them,  and  thus 
render  a breach  less  practicable,  since  the  whole,  or  a por- 
tion, of  the  parapet  will  st|ll  retain  its  place  after  the  breach 
has  been  made  in  the  scarp,  depending  on  the  distance  at 
which  the  parapet  has  been  moved  back. 

In  all  of  these  cases  oflthe  application  of  the  independ- 
ence of  the  parapets,  Chpumara  proposes  to  convert  the 
space  left  between  the  f^ot  of  the  parapet  and  the  scarp 
wall  into  a chemin  de  ron^e^  or  corridor,  which  is  covered 
in  front  by  a slight  para|>et,  and  from  enfllading  Are  b}^ 
giving  an  increased  heigllt  to  the  portfon  of  the  parapet 
adjacent  to  the  salients,  forming  a honnet^  as  in  Figs.  1,  a, 
B,  etc.  This  corridor  is  ocfeupied  by  sharpshooters  to  annoy 
the  besieger’s  trenches,  furthermore,  Choumara  regards 
the  corridor  as  an  additional  security  against  surprise  and 
escalade.  I 

2.  Choumara  proposes  to^place  high  traverses  in  the  bas- 
tion salients,  to  cover  the  fa^es  from  enfilade  and  the  flanks 
from  reverse  views,  and  sinijlar  traverses  at  the  shoulder 
angles  with  the  same  object.  These  he  also  proposes  to 
casemate,  or  else  construct  with  blindages  for  artillery  to 
obtain  a fire  in  the  directionk  of  the  capitals,  and  reverse 
views  on  the  demi-lune  glacis  and  the  breach  in  the  bastion 
face.  As  these  traverses,  from  their  height,  might  give  the 
besiegers  in  possession  of  tliemta  plunging:  fire  on  the  bastion 

t 


I. 

J 


I 


64 


klh:mp:nts  of  permanent  fortification. 


retrenchments,  he  proposes  so  to  arVange  them  that  they  cair 
he  readily  destroyed  at  any  momont  by  mines,  or,  if  of  tim- 
ber, be  burned.  / 

3.  To  mask  the  masonry  of  |me  enceinte  and  demi-lune 
from  breaching  batteries,  erected  in  their  usual  positions 
along  the  crests  of  the  glacis,  phoumara  proposes  to  form 
what  he  terms  an  interior  gla(^s^  or  covering  mass  of  earth, , 
in  the  ditches,  the  crests  of  which  shall  mask  the  masonry 
of  the  scarps  from  the  positions  in  question  ; and  the  upper 
surface  of  which,  forming  a/ glacis,  shall  be  swept  by  the 
tire  of  the  works  in  its  rear.  I In  this  manner  he  expects  to 

/difficult  operation  of  making 
)tain  suitable  positions  for  their 


>f  his  outworks  those  points  on 
favorable  to  the  action  of  the 
proposes  in  this  way  to  cripple 


force  the  besiegers  to  the 
lodgments  in  this  glacis  to 
breaching  batteries. 

4.  By  selecting  for  some 
the  exterior  which  are  niosj 
assailant’s  sharpshooters,  h( 
this  important  means  of  attack. 

5.  By  giving  greater  ex:ent  to  the  exterior  side,  and  a 
more  retired  position  to  the  curtain,  which  is  also  to  be 
made  as  short  as  possible,  Choumara  obtains  bastions  of 
ample  size,  not  only  to  admit  of  the  modifications  he  pro- 
poses for  the  parapets,  traverses,  and  chemms  de  ronde^  but 
for  strong  interior  retrencl  ments,  so  organized  with  bomb- 
proof shelters,  and  arraiq  ed  defensively  towards  the  in- 
terior, that  each  bastion  w:  II  admit  of  a defence  to  the  rear 
at  its  gorge,  after  the  besi  sgers  may  have  efiected  a breach 
at  other  points  and  penetrated  within  the  enceinte. 

110.  Plan.  In  adapting  these  propositions  for  a bas- 
tioned  front,  Choumara  pipposes,  in  order  to  obtain  the  re 
quisite  room  in  the  intericf*  of  the  bastions  and  a large  in- 
crease of  flank  fire,' to  takefthe  exterior  side  from  400  to  600 
metres,  French.  In  the  fiiput  (Fig.  1,  PI.  12),  for  example, 
the  exterior  side  is  440  i:|ietres ; the  lines  of  defence  are 
drawn  through  a point  on  "Ihe  perpendicular  of  the  front  at 
74  metres,  or  one-sixth  of  440  metres  within  the  exterior 
side  ; the  faces  are  150  metres,  and  the  flanks,  drawn  per- 
pendicular to  the  lines  of  defence,  are  85  metres,  a length 
which  prolongs  them  35  metres  within  their  intersections 
with  the  lines  of  defence. 

By  this  construction  the  curtain,  which  will  be  115  metres 
long,  will  be  well  swept,  and  the  gun  at  the  curtain  angle 
can  be  brought  to  bear  on  the  one  of  the  besieger’s  counter- 
battery against  the  flanks  which  is  furthest  out,  thus  giving 
a very  great  preponderance  in  tire  to  the  flank  over  the 
counter-battery. 


ELEMENTS  OP  PERMANENT  FORTIFICATION. 


G5 


The  deep  reentering  thus  foymed  between  the  flanks  and 
curtains  gives  ample  room  iovk  tenaille  with  flanks  for  four 
guns;  these  guns  are  coverecy  in  flank  by  a traverse.  The 
tenaille  is  not  revetted  in  front  of  its  curtain  and  flanks,  or 
at  its  gorge.  It  masks  suftifciently  the  scarp  of  the  flanks, 
and  curtain  of  the  enceinta,  to  prevent  any  danger  to  the 
latter  from  the  destruction  pi  the  portion  of  the  scarp  wall 
that  can  be  seen  over  the  tinaille. 

111.  The  salient  of  tik  demi-lune  is  the  vertex  of  an 
equilateral  triangle,  the  Base  of  which  is  drawn  between 
two  points  on  the  bastijn  faces,  at  18  metres  from  the 
shoulder  angles.  The  flees  of  the  demi-lune,  d,  are  111: 
metres,  and  revetted.  The  parapet  of  the  demi-lune  is 
thrown  back  from  the  yevetment,  leaving  a corridor  cov- 
ered by  a parapet  at  tie  foot  of  its  exterior  slope.  The 
parapet  is  broken  nearithe  gorge,  so  as  to  give  two  short 
flanks  of  13  metres  perpendicular  to  the  exterior  side.  The 
salient  is  occupied  by  I casemated  traverse  with  flanks  for 
three  guns.  This  traverse  masks  the  interior  of  the  demi- 
lune and  the  corridor  from  enfilading  views.  A disposition 
is  shown  for  cuts  acro^^  the  demi-lune  faces,  the  parapets  of 
which  are  to  be  throwi  up  after  the  siege  commences.  The 
demi dune  ditch  is  17?  metres  wide.  The  portion  of  this 
ditch  towards  the  gorge  slopes  upward  as  a glacis,  and  is 
swept  bv  the  fire  of  the  enceinte. 

112.  The  interior  glacis  of  the  demi-lune  commences  at  the 
counterscarp  of  this  wbrk  and  has  a glacis  slope  outwards, 
its  width  being  45  metres.  Here  commences  the  revetted 
gorge  of  the  covered-way.  The  width  of  the  covered-way  is 
10  metres.  Its  interior  crest  is  an  indented  line.  There  are 
no  traverses  in  this  work  unless  required  for  its  defilement. 

113.  A spacious  and  strong  reduit  is  placed  in  the  demi- 
lune salient  place-of-arms.  Its  faces  are  132  metres  long, 
and  revetted.  Its  parapet  is  thrown  back,  leaving  a corridor 
in  front  of  it,  and  is  curved  at  the  salient  for  five  guns, 
sweeping  along  the  capital.  A bonnet  is  placed  in  its  salient 
to  cover  the  corridor  from  enfilade,  and  two  traverses  for  tlie 
same  object  on  its  terre-plein.  This  reduit  forms  a mask 
for  the  portion  of  the  demi  lune  occupied  by  the  traverse. 

114.  Choumara  places  strong  reduits,  m,  with  revetted 
scarps  and  gorges  in  the  reentering  place-of-arms.  The  para- 
pets of  these  works  are  curved  at  the  salients  for  batteries  to 
sweep  the  approaches  on  the  bastion  capitals  and  the  demi- 
lune glacis,  and  they  are  thrown  back  from  the  scarp  walls 
to  give  a corridor  for  sharpshooter.s.  As  these  reduits  are 


66  ELEMENTS  OF  PERMANENT  FORTIFICATION. 

/ 

necessarily  contracted,  Chonmara  prefers  to  them  a strong 
reduit  of  larger  dimensions,  placed  in  the  bastion  salient 
p1ace-of-arms  and  organized  like  the  preceding. 

115.  One  of  the  mos|  striking  features  of  Choumara’s 
rnoditications  is  the  mod^  in  which  he  proposes  to  organize 
the  large  bastions,  with^defences  which  shall  serve  as  an  in- 
terior retrenchment,  in  case  the  bastion  is  one  of  the  points 
of  attack;  or  convert,  the  bastion  into  an  isolated  fort  or 
citadel  for  the  garrison,  in  case  the  besieger  gains  possession 
of  the  interior  of  the  enceinte  through  an  assault  at  some 
other  point.  This  he  proposes  to  accomplish  bj  increasing 
the  lengths  of  the  exterior  side,  and  also  of  the  bastion  Hanks. 

116.  With  tliis  object  Choumara  places  a row  of  case- 
mates within  the  bastions,  on  a line  perpendicular  to  their 
capitals.  Each  ca'semate  is  from  60  to  80  feet  long,  from 
12  to  20  feet  wijde,  and  12  feet  high.  This  row  of  case- 
mates serves  as  a curtain  both  for  the  retrenchment  of  the 
bastion  and  for  ihe  defence  of  the  gorge  against  an  interior 
attack.  For  the  defence  of  the  salient  portion  of  the  bas- 
tion a cut  is  ^ade  across  each  face  and  extended  to  the 
capital.  The  $carp  of  this  cut  is  made  into  the  form  of  a 
bastion  front  pith  orillons  at  the  shoulder  angles;  the  case- 
mates forming  the  curtain  of  this  front.  The  counterscarp 
of  the  cut  msfj  be  either  revetted,  or  have  a simple  slope  of 
earth.  In  tlie  latter  case  the  bottom  of  the  ditch  of  the 
front  at  the  foot  of  the  scarp  wall  is  at  a suitable  level  to 
admit  of  an  efficient  height  of  scarp  wall  to  secure  it  from 
escalade.  Aj  broad  ramp  leads  from  the  centre  casemate, 
along  the  capital,  towards  the  bastion  salient,  to  the  counter- 
scarp of  the  lent,  and  there  branches  into  two  other  ramps 
leading  up  to  the  bastion  terre-plein  on  the  right  and  left. 
Until  the  besiegers  are  about  to  breach  the  bastion  faces 
their  parapets  are  left  intact ; and  the  portions  of  the  cut 
along  which  the  parapets  run  are  filled  up,  as  in  the  bastion 
on  the  right,Uhus  leaving  a free  communication  throughout 
the  interior  of  the  bastion.  So  soon  as  it  is  thought  neces- 
sary to  cut  ofPthis  communication  and  to  get  the  retrenched 
portion  in  a state  of  defence,  that  part  of  the  parapet  across 
the  cuts  is  demolished  ; the  cut  excavated  and  suitably 
arranged  ; and  the  parapet  of  the  retrenchment  fornied  in 
]\arr  of  the  earth  arising  from  these  changes.  The  para- 
pet of  the  front  of  the  retrenchment  is  thrown  back,  leaving 
a corridor  for  sharpshooters  covered  by  a slight  parapet ; 
that  portion  of  this  corridor  along  the  retired  flank  being 
covered  by  the  earthen  mask  of  the  orillon.  Choumara 


ELKMKNTS  OF  PERMANENT  FORTIFICATION.  67 

further  proposes,  where  there  is  a probability  of  the  scarp 
of  the  bastion-face,  which  closes  the  cut  on  the  exterior, 
being  opened,  so  that  a breach  might  be  made  by  firing 
through  it  on  the  flank  of  the  retrenchment,  to  run  the 
scarp  wall  of  the  retrenchment  at  right  angles  across  the 
cut,  as  shown  on  the  right  face  of  the  left  Bastion,  and  to 
arrange  the  bastionnet,  which  this  modification  would  give 
at  the  shoulder  angle,  for  sharpshooters. 

117.  To  expose  the  interior  of  the  retrenchment  to  the 
fire  of  the  flanks  of  the  ad jacent  bastions,  and  to  the  parapet 
of  a second  retired  interior  retrenchment  resting  on  the  two 
curtains  adjacent  to  the  bastion  of  attack,  a portion  of  the 
parapet  of  the  bastion  fianks,  near  the  curtain,  is  demol- 
ished, and  a slope  is  given  to  the  portion  of  the  terre-plein 
on  which  it  rested.  The  retirefl  interior  retrenchment 
Choumara  proposes  to  make  of  e^rth  in  the  form  of  a bas- 
tioned  front,  breaking  the  faces  iij  the  most  suitable  manner 
to  sweep  the  rear  of  the  retrenchi|ient  in  its  front. 

118.  The  dispositions  for  corfverting  the  bastion  into  a 
citadel  are  similar  to  the  preceding,  consisting  of  a small 
front,  the  faces  of  which  are  nearly  in  the  prolongations  of 
the  adjacent  curtains,  with  orill(|ns  to  cover  the  corridor  of 
the  retired  flank.  This  front  his  a covered-way  and  glacis 
in  advance  of  it,  the  crest  of  whjch  masks  the  scarp. 

119.  Choumara  has  made  afi  ample  provision  for  easy 
communications  between  all  points  of  the  enceinte  and  the 
outworks,  so  placing  them  as  tb  be  well  covered  from  the 
besieger’s  fire  and  well  swept  by  that  of  the  garrison  ; pre- 
ferring wide  ramps  for  this  puifpose.  The  communication 
from  the  enceinte  with  the  maiiji  ditch  is  through  gateways 
in  the  scarp  wall  of  tlie  curtain,  at  its  extremities.  The 
rampart  at  these  points  is  removed  to  the  level  of  the  main 
ditch  ; the  portion  of  it  betweefi  them,  along  tlie  centre  of 
the  curtain,  being  sustained  at  tfie  ends  by  revetment  w^alls 
run  back  perpendicularly  to  th4  scarp  wall  of  the  curtain; 
Ramps  lead  from  the  gorges  of  the  bastions  down  to  these 
outlets  into  the  main  ditch.  From  these  outlets  the  com- 
munications to  the  outworks  aip  around  the  fianks  of  the 
tenaille,  and  through  the  enceinte  ditch,  to  ramps  placed 
along  the  enceinte  counterscarp  Heading  into  the  demi  lune, 
the  demi-lune  ditch,  the  enceinte  covered-way,  and  its  re- 
doubts in  the  places-of-arms  ; aud  from  the  demi  lune  ditch 
to  the  redoubt  of  the  demi-|lune  salient  place  of-arms. 
Posterns  on  the  faces  and  fianks  of  the  bastions,  near  the 
shoulder  angles,  lead  to  the  corridors  of  the  enceinte.  Pas- 
. sages  are  left  at  the  ends  of  the  faces  of  the  outworks  lead- 


68 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 

ing  from  their  corridors  to  tjle  interior  of  the  works.  To* 
Keep  open  the  communication  between  the  bastions,  a gal- 
lery lietween  their  gorges  is  made  along  the  curtain  wall. 

For  the  security  of  the  . casemates,  barricades  can  be  made 
in  their  doors  and  windows,  by  means  of  timber  let  in 
grooves  made  in  the  walls ; the  space  between  the  exterior 
and  interior  timber  facing  being  tilled  with  sand-bags. 

120.  Kemarks.  jhe  memoirs  in  which  Choumara 
brought  his  propositions  before  the  public  naturally  attracted 
attention,  as  much,  perhaps,  from  their  polemical  character 
and  piquancy  of  style  as  their  professional  interest.  They 
contain  but  few  things  the  germs  of  which  are  not  to  be 
found  in  writers  wiho  preceded  him. 

His  moditicatiops  respecting  the  parapets,  throwing  them 
back  from  the  scarps  and  breaking  them  into  directions 
best  suited  for  defence,  are  to  be  met  with  in  Chasseloupe^ s 
propositions.  / 

His  proposals;  for  lengthening  the  bastion  flanks  and 
occupying  the  s|ilient  places-of-arms  by  redoubts  with  con- 
siderable command,  are  to  be  found  in  the  method  of  de  la 
Cl  ache.  | 

To  Virgin  he  seems  to  be  indebted  for  his  organization 
of  interior  retrenchments,  which  are  to  con  vert  each  bastion 
into  an  independent  work,  equally  provided  for  defence 
against  approaches  both  from  the  interior  and  exterior  of 
the  enceinte.  | 

Like  disputants,  usually,  of  an  ardent  temperament,  he 
over-estimates ; the  value  of  many  of  his  propositions  and 
loses  sight  of  their  countervailing  defects.  By  laying  down 
as  a principle  what  may  be  exceptionally  good  in  practice, 
he  has  rather  weakened  his  own  positions.  This  is  the  ciu  e, 
particularly,  with  his  rule  of  independence  of  the  parapets, 
on  the  scarps,  which,  if  adopted  in  all  cases,  might  demand 
a greatly  increased  and  hurtful  command,  and  cut  up  to 
great  disadvantage  the  interior  spaces  of  the  bastions. 

His  introduction  of  the  chemins  de  ronde  on  the  faces  of 
the  bastion  and  the  demi-lune  adds  really  very  little,  if  at 
all,  to  the  exterfcr  defence  ; whilst  they  contract  the  interior 
space  of  these  ’Iporks,  break  in  upon  the  unity  of  the  de- 
fence, and  place  |the  troops  in  them  in  a very  exposed  posi- 
tion to  the  meanly  of  annoyance  possessed  by  the  besieger. 

His  expectations  with  respect  to  the  effect  of  his  tire  in 
the  direction  of  the  capitals,  in  delaying  the  besieger’s  ap- 
proach to  the  3d\  parallel,  were  hardly  warranted  by  the 
experience  gained \ in  artillery  and  small  arms.  e\-en  at  the 
time  the  Iasi  editing  of  his  memoirs  appeared.  It  is  hardly 


eli-:mhnts  of  permanent  fortification. 

/ 


69 


to  be  questioned,  now  that  thesb  weapons  have  been  so 
greatly  improved,  both  in  range  and  accuracy  of  fire,  that, 
considering  the  increased  development  of  the  besieger’s 
parallels,  which  gives  him  a choice  of  positions  for  his  bat- 
teries on  so  extended  a line,  thb  concentrated  fire  he  could 
bring  to  bear  on  the  batteries  jn  question  would  not  only 
soon  ruin  their  casemates,  but  would  greatly  damage  the 
adjacent  faces  and  also  the  fianbs  of  the  bastions,  although 
covered  from  enfilading  view^,  either  by  the  direction  of 
the  parapets  of  the  faces,  or  t^e  high  traverses  raised  with 
the  same  object. 

These  advantages  in  the  jDosition  of  the  besieger,  it  is 
thought,  would  prevent  any  oelay  in  pushing  forward  his 
approaches  up  to  the  3d  parallel.  After  this  the  approaches 
would  probably  be  retarded  ^beyond  the  usual  time  in  the 
attack  on  Cormontaigne’s  front,  owing  chiefly  to  the  reduits 
in  the  bastion  and  demi  lune  jsalient  places  of-arms,  and  the 
arrnngement  of  the  face-covei*  in  the  enceinte  ditch. 

121.  Supposing  an  enceinte  organized  according  to  his 
method,  and  containing  intqHor  retrenchments  to  oppose 
the  besieger’s  approaches  bol|i  from  without  and  within  the 
enceinte,  Choumara  estimate|  at  least  six  separate  epochs  of 
bleaching  batteries,  as  follow^  : 

1st,  against  the  reduit  of  |be  demi-lune  salient  place  of- 
;arms.  I 

2d,  against  the  demi-lune  |ind  the  reduit  of  the  bastion 
salient  places-of-arms.  | 

3d,  against  the  bastions.  | 

4th,  against  the  bastion  retrenchment;  5th,  against  the 
retired  retrenchment. 

6th,  and  finally,  against  th^  bastions  converted  into  cita^ 
dels  by  the  fronts  with  which|their  gorges  are  closed. 

According  to  the  estimate  of  the  time  made  by  Choumara, 
the  time  between  opening  the  ltrenches  and  the  final  assauh 
would  be  nearly  three  times  al  great  as  it  would  be  in  Cor. 
raontaigne’s  method.  \ 

122.  The  complications  of  this  method  unfitted  it  for 

practical  application,  even  at  tne  time  of  its  design,  and 
render  it  useless  as  a fortification  to  oppose  modern  arms. 
It  combines,  however,  many  of  he  features  introduced  into 
permanent  works  by  the  best  engineers  who  had  lived 
previous  to  the  date  of  its  defign,  and  a large  number 
which,  with  changes  in  dimensions  only,  are  to  be  found  in 
the  most  recently  constructed  outworks  and  detached  forts. 
While  as  a system  it  is  obsolete,  its  details  are  well  worth 
etudv.  ! 


70 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


CHAPTER  III. 

TENAILLED  SYSTEM. 

123.  Several  engineers  of  professional  eminence  have 
proposed  tenailled  enceintes,  as  offering  defensive  properties 
superior  to  bastioned  enceintes.  This  system  has  found  but 
few  advocates,  and,  except  in  particular  localities,  where  the 
natural  features  of  the  site  demanded  it,  and  for  small  works, 
it  has  met  with  no  practical  applications. 

Requiring  that  the  salient  angles  shall  not  be  less  than  60°, 
and  the  reentering  angles  between  90°  and  100°,  the  tenail- 
led system  is  only  adapted  to  regular  polygons  of  a sufficient 
number  of  sides  to  admit  of  these  conditions  being  satisfied. 

If  the  exterior  sides  are  kept  within  the  limits  usually 
admitted  by  engineers  for  bastioned  enceintes,  the  faces  of 
the  tenailles  become  very  long,  and  the  reenterings  very  deep  ; 
thus  presenting  two  serious  defects — long  lines  which  are 
very  much  exposed  to  enfilade,  and  a great  diminution  of 
the  interior  space,  as  compared  with  the  bastioned  enceinte. 

The  ditches  when  dry  can  only  be  swept  by  casemated 
defences  in  the  reentering  angles;  and  even  then  but 
partially,  unless  the  casemated  embrasures  are  placed  very 
near  the  level  of  the  bottom  of  the  ditch,  in  which  case  the 
enceinte  would  be  exposed  to  a surprise  through  the  em- 
brasures ; and,  in  the  contrary  case,  liable  to  a like  attempt 
from  the  dead  space  at  the  reenterings  below  the  embrasures. 
In  wet  ditches  this  exposure  to  surprise  would  be  much  less 
if  the  ditches  could  not  be  forded.  In  either  case  the  de- 
fect arising  from  embrasure  casemates  placed  in  a reenter- 
ing angle  would  be  a serious  objection  to  using  the  guns  of 
each  side  simultaneously. 

When  the  salient  angles  of  the  tenailles  are  acute,  the 
effect  of  the  enfilading  fire  would  not  be  felt  alone  on  the 
face  enfiladed,  but  on  the  adjacent  face  or  front,  and  shot 
passing  over  would  damage  the  adjacent  tenailles. 

The  foregoing  are  the  chief  objections  to  this  system.  It 
presents  no  advantage  but  the  very  illusory  one,  considering 
the  consequences  arising  from  it,  of  long  faces  presenting  a 
mutual  flanking  and  cross  fire  of  considerable  extent. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


71 


CHAPTER  lY. 


POLYGONAL  SYSTEM. 

I. 


POLYGONAL  SYSTEM. 

124.  The  polygonal  system  had  previously  been  pro- 
posed by  several  engineers  of  distinction,  but  its  most  ardent 
advocate  was  the  celebrated  Montalembert,  born  1714, 
died  1800,  whose  views  have  been  more  or  less  carried  out 
in  many  of  the  constructions  of  Germany  since  his  time. 

Consisting  of  either  a simple  polygonal  enceinte  without 
reenterings,  the  sides  of  which  are  flanked  by  casemated 
caponnieres,  placed  at  the  middle  point  of  the  fronts,  or  of 
fronts  either  slightly  tenailled  or  of  a bastion  form,  with 
short  casemated  flanks  to  flank  the  faces  of  the  central 
caponnieres,  this  system  affords  more  interior  space,  and 
from  the  mode  adopted  of  flanking  the  enceinte,  will  admit 
of  much  larger  fronts  than  either  the  bastioned  or  the 
tenailled  systems.  The  salient  angles  moreover  will  be 
more  open  in  this  than  in  the  other  two  systems. 

From  these  peculiarities  of  this  system  the  positions  suit- 
able for  the  erection  of  batteries  to  enfilade  the  faces  of  the 
enceinte  are  less  advantageous,  from  their  being  thrown  in 
nearer  to  the  ad  jacent  fronts  than  in  either  of  the  other 
systems ; whilst  a greater  development  of  trenches  will  also 
be  requisite  to  envelop  the  fronts  of  attack. 

These  obvious  advantages  for  the  distant  defence,  how- 
ever, are  counterbalanced  to  some  extent  for  the  close  de- 
fence by  the  want  of  the  concentrated  cross-fires  which  are 
afforded  by  the  enceinte  itself,  in  both  the  bastioned  and 
tenailled  systems,  in  advance  of  the  salients,  and  upon  the 
ground  generally  in  advance  of  the  fronts.  ' 

Each  front  of  the  polygonal  system  when  its  angles  are 
acute  offers  moreover  a long  line  to  enfilading  and  slant  fire 
which  takes  the  adjacent  front  in  reverse. 


72 


ELEMENTS  OF  PEKMANENT  FOKTIFICATIOK. 


But  the  chief  objection  to  tliis  system  lies  in  the  mode 
adopted  for  tianking  the  enceinte.  The  casemated  capon- 
nieres  for  this  purpose  being  exterior  to  the  enceinte,  it  will 
be  exposed  to  escalade  as  soon  as  the  fire  of  the  caponnieres 
is  silenced,  which,  considering  the  structure  formerly 
adopted  for  them  and  the  exposure  of  their  embrasures  to 
the  enfilading  batteries,  would,  in  all  probability,  take  place 
at  an  early  period  after  this  fire  is  opened. 

These  defects  in  masonry  caponnieres  have  been  removed 
in  some  degree  as  previously  described,  and  those  of  iron 
and  steel,  constructed  and  proposed,  will  probably  resist  the 
most  vigorous  attack  of  the  assailant.  The  advantages  of  this 
system  in  its  modern  methods  have  led  to  its  almost  uni- 
versal adoption.  The  new  forts  around  Paris  are  polygonal 
in  their  traced) 


i 

i 

r 


II. 


montaeembekt’s  "^polygonal  method. 


wliose  works  have  had  an 
ress  of  the  art,  Montaleih 


125.  Among  the  writers  on  permanent  fortification 


although  not  educated  a^  an  engineer. 


important  bearing  on  the  prog- 
bert  holds  a conspicuous  place. 
Struck  by  the 
evident  defects  of  the  nu  thods  of  his  predecessors,  partic- 
ularly the  want  of  casema  es,  both  for  defensive  dispositions 
for  artillery  and  musketr>^,  and  the  shelter  of  the  garrison 
and  munitions,  Montalem  3ert  devoted  his  time,  talents,  and 
fortune  to  bringing  about  a change  in  the  direction  in  whhdi 
it  seemed  to  him  called  f >r.  His  efforts,  howevei*,  led  to  no 
modifications  of  conseqi  enee  during  his  life,  which  was 
principally  spent  in  angr^’  controversies  with  his  opponents, 
except  the  extension  ot  casemated  defences  for  sea-coast 
works  ; but  after  the  ter:  [lination  of  Kapoleon’s  wars  a new 
school  of  engineers  grew  ij)  in  Germany,  based  mainly  upon 
the  views  put  forth  by  Montalem bert,  which  views  met 
favor  in  other  parts,  altliough  still  opposed  by  many  able 
engineers  in  all  countries  Who  contested  their  soundness. 
The  principal  propositions  of  Montalembert  consist : 

1.  In  the  entire  rejectioii  of  the  bastioned  system,  as,  ac- 
cording to  his  views,  unsuitable  to  a good  defensive  disposi- 
tion ; and  in  its  stead  he|  proposed  to  use  either  the  te- 
nailled  system^  or  else  the  polygonal  system. 


/ 


ELEMENTS  OF  PERi^NENT  FORTIFICATION. 


2.  In  basing  the  streng|b  of  these  last  systems  upon  an 
overwhelming  force  of  artf llery  fire  in  defensive  casemates. 

3.  In  organizing  strona  permanent  works  within,  and  in- 
dependent of  the  body  of  the  place,  wliich  are  to  serve  as  a 
secure  retreat  for  the  g|rrison  when  forced  to  give  up  its 
defence. 

Most  of  the  objection!  urged  against  thebastioned  system 
and  its  outworks  having  already  been  adverted  to  in  the 
analysis  of  the  front,  i^will  be  unnecessary  to  recapitulate 
tenailled  system,  composed  of  faces 
eentering  angles  of  90°,  and  salient 
ed  by  Montalembert  'perpendicular 
position  of  the  faces  at  the  reenter- 
ings, has  many  obvio|s  and  more  serious  defects  than  either 
of  the  other  two,  it  i|  proposed  to  give  hei’e  a description  of 
alone,  and  that  in  its  most  simple 
ich  Montalembert  presented  it  for  tlie 
ourg,  one  of  the  most  important  naval 


them  here ; and  as  th< 
of  equal  lengths  with 
angles  of  60°,  and  ter| 
fortification^  from  tl 


the  polygonal  systei 
form — the  one  in  wl 
fortifications  at  Cher| 

■stations  in  France. 

126.  Montalembert  first  gave  the  name  polygonal  system 
to  a trace  of  the  enceinte  in  whi(^h  all  of  the  angles  are 
•either  salient,  or  where  the  reentering  are  very  slight. 

Plan.  In  the  trace  proposed  forjthis  place,  x,  y,  (Fig.  1, 
PI.  13,)  is  the  exterior  side,  or  magistral  of  the  scarp.  The 
body  of  the  place  consists  of  the  scarp  wall,  d.  Fig.  1 and 
■ section  on  p q,  arranged  with  caseinates  for  artillery  and 
musketry;  of  a corridor,  c,  between  these  casemates  and  the 
earthen  rampart  and  parapet,  b.  In  rear  of  the  rampart  is  a 
high  wall,  A,  arranged  with  loop-hole  ?,  within  which  the  gar- 
rison  retires  when  driven  from  the  ( efence  of  the  rampart. 

Casemated  caponnieres,  m,  which  gire  secured  from  a coup- 
de-rnain^  are  placed  along  the  rampait,  and  so  arranged  that 
a fire  can  be  thrown  from  them  pver  the  parapet  and 
also  along  the  terre-plein.  The  corridor,  c,  is  also  swept  by 
a casemated  caponniere,  g,  for  muskAry;  and  the  front  of 
the  wall.  A,  by  a like  arrangement.  i 

The  principal  caponniere  for  flankiiig  the  main  ditch  is  in 
the  form  of  a lunette,  and  placed  at  tlie  middle  of  the  exte- 
rior side,  its  fianks  joining  the  casemited  gallery,  d,  of  the 
enceinte.  The  flanks,  h,  and  the  faces,  k,  of  this  work,  are 
arranged  with  two  tiers  of  artillery  and  musketry  fire  ; each 
flank  carrying  ten  guns  and  each  face  twelve  guns.  A wet 
ditch,  i,  separates  the  faces  and  flanks ; a loop-holed  wall 
encloses  the  portion  between  the  flainks,  from  which  the 
opposite  portion  between  the  faces  is  (swept  by  musketry. 


74 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


The  caponoiere  is  covered  in  front  by  a face  cover,  n,  of 
earth,  in  the  shape  of  a redan.  The  scarp  of  the  enceinte  is 
covered  in  like  manner  by  the  continuous  face-cover,  o,  of 
earth,  in  the  reentering  angles  of  which  casemated  batteries 
of  two  stories,  for  artillery  and  musketry,  are  placed  to  llarik 
the  ditches  and  sweep  the  positions  for  counter- batteries 
around  the  salients  of  the  covered-Vv  ay.  These  batteries  are 
masked  in  front  by  the  earthen  w/rks,  s and  q.  The  whole 
is  covered  by  the  glacis  of  the  co/^ered-way,  arranged  in  the 
usual  manner.  f 

The  better  to  flank  the  main  capon niere,  the  portion  of 
the  casemated  gallery  joining/it  is  arranged  with  two  tiers 
of  artillery  fire,  the  remaining  portion  having  but  one  tier- 
of  guns.  / 

127.  Profiles.  The  sections  along  p q,  r s,  and  t u, 
show  the  relative  command  of  the  diflerent  works  and  the 
width  of  the  ditches  and  e/rthen  ramparts. 

The  communications  between  the  different  works  are  by 
bridges  across  the  wet  dijfches. 

128.  It  is  now  generjilly  admitted  that  although  Monta- 

lembert  has  rendered  i important  services  to  the  progress  of 
fortification,  particular!^  as  regards  the  more  extensive  em- 
ployment of  casematecf  defences,  still  many  of  his  projects- 
were  visionary.  | 

Many  of  the  details |of  his  system  in  the  state  of  develop- 
ment in  which  he  left!  it  may  be  said  to  have  become  obso- 
lete without  being  subjected  to  trial  by  the  guns  which  it 
was  designed  to  resisff 

The  improvement  jn  artillery  having  rendered  the  com- 
plete masking  of  ma^nry  obligatory,  compelled  the  advo- 
cates of  the  polygonal  system  to  introduce  many  modifica- 
tions to  accomplish  t!|is  object. 

129.  Among  thes^  advocates.  General  Brialmont  of  the 
Belgian  engineers,  boyn  1821,  has  in  his  writings  and  long- 
experience  in  the  construction  of  fortifications,  particularly 
those  of  Antwerp,  coi|tinued  the  development  and  improve- 
ment of  the  system  u|)  to  the  present  time.  He  proposes- 
in  his  latest  works  the|extensive  use  of  iron  and  steel  case- 
mates and  turrets  at  iniportant  points,  and  in  his  earlier  con- 
structions displayed  gi^at  skill  in  masking  masonry  from 
the  besiegers’  fire. 

130.  The  defences  of  Antwerp  planned  and  carried  on 
under  his  direction  since  1859  exemplify,  better  than  any 
other  large  work,  the  latest  applications  of  the  polygonal 
system  with  its  outworks.  Plate  11,  Figs.  2,  3,  4,  5,  6 and 


ELEMENTS  GF  PERMANENT  FORTIFICATION. 


75' 


T,  show  a half  of  one  of  these  fronts  of  which  the  exterior 
side  is  1000  metres.  The  references  and  dimensions  are  in 
metres. 

The  ditches,  which  are  wet,  are  from  50  to  80  metres 
wide  and  from  2 to  3 deep.  They  are  flanked  by  a central 
capunnito’e  which  is  itself  defended  by  the  first  and  second 
flanks  of  the  enceinte.  These  are  protected  from  front  Are 
by  being  broken  back  and  covered  by  orillons. 

At  the  middle  of  the  curtain  is  a defensible  barrack, 
which  serves  as  a cavalier  and  retrenchment,  and  whose 
front  is  masked  by  the  caponniere  and  its  wings. 

The  caponniere  is  covered  by  the  counterguard,  in  front  of 
whose  ditch,  which  is  dry,  and  15  metres  wide,  is  a ravelin 
with  a ditch  and  covered- way^ 

The  ravelin  ditch  is  flanked  by  casemated  low  batteries^ 
serving  as  keeps  for  the  reentering  placemf-arms. 

The  salient  of  the  capoflniere,  the  salient  angle  being 
about  60°,  is  95  metres  from  the  exterior  side.  The  cur- 
tain is  65  metres  within  the  exterior  side  and  is  330  metres 
in  length. 

The  first  and  second  flanks  have  a length  of  31^  and  11 
metres  respectively.  Th^y  are  designed  to  flank  the  faces 
and  gorge  of  the  caponniere,  its  flanks  being  swept  by  the 
fire  of  its  wings.  / 

The  curtain  is  made  pp  of  two  half  curtains  and  a de- 
fensible barrack  separated  from  each  other  by  roadways 
leading  by  bridges  to  Ae  low  terre-plein  in  rear  of  the 
caponniere. 

The  flanks  of  the  caponniere,  which  have  two  tiers  of 
casemates,  are  separate^  by  a court  70  metres  long,  10 
metres  wide  at  its  outer  jextremity,  and  16  metres  at  the  ex- 
terior side.  I 

Its  wings  are  broken  |)ack  and  provided  with  a traverse 
as  shown.  ] 

The  defensible  barrac]^  is  of  the  form  shown  in  the  fig- 
ure. The  length  of  itsjhead  is  such  that  it  is  masked  by 
the  wing  of  the  capondiere  and  the  orillon.  Its  flanks 
make  an  angle  of  aboul  100°  with  the  head,  and  are  75 
metres  long.  The  gorg^  is  closed  by  masonry,  forming  a 
keep  for  the  front. 

The  salient  of  the  cou^terguard  is  165  metres  from  the 
exterior  side,  and  that  of  the  ravelin  270  metres.  The  dis- 
tance, K D,  is  175  metres,  ^nd  k b,  225. 

The  magistral  of  the  low  battery  flanking  the  ravelin 


76  ELEMENTS  OF  PERMANENT  FORTIFICATION. 

ditcli  has  a length  of  50  metres,  and  n^akes  an  angle  of  120° 
with  that  of  the  ravelin.  / 

The  covered-way  of  the  main  work  is  20  metres  wide, 
that  of  the  ravelin  from  8 to  14  pietres,  and  arranged  as 
shown. 

The  parapet  of  the  ravelin  is  broken  as  shown,  to  prevent 
eniilade  and  is  provided  with  a traverse  and  a “ reverse  bat- 
tery” near  the  salient,  sweeping  the  ground  in  front  of  the 
salient  of  the  main  work,  which  salient  usually  contains  a 
cavalier. 

The  communications,  which  are  shown  in  the  plan,  are 
direct,  broad,  and  well  protected. 

The  sections  give  the  profiles  of  the  enceinte  and  its  out- 
works. Fig.  5,  section  on  shows  a modification  of  the 
defensible  barrack  proposed  by  Brialmont,  to  give  better 
protection  to  the  masonry. 

The  parapets  are  generally  8 metres  thick.  The  case- 
mated  quarters  will  accommodate  2000  men. 

This  enceinte  is  strengthened  by  a belt  of  polygonal  de- 
tached forts  placed  in  defensive  relations  with  each  other  at 
R distance  of  about  IJ  miles  apart,  and  from  2 to  3 miles 
from  the  enceinte.  ? 

Note. — Full  descriptions  of  ^lie  details  of  this  front,  with  an  analysis 
of  its  different  parts  and  some  proposed  modifications,  will  be  found  in 
Brialmont,  “Traite  de  Fortificiition  Polygonale,”  Paris,  1869. 


ELEMENTS  OF  PERMANENT  PORTIFIGATION.  77’ 

* 

/ 

/ 

/ 

/ 


CHAPTEE  f. 

/ 

EXISTING  GERMAN  FORTIFICATIONSr 

I.  ^ 

i 

RECENT  aERMAN  FORTIFICATIONS. 

j 

131.  In  the  large  additions  |nade  to  the  fortifications  of 
the  German  States,  between  tl^  general  peace  in  Europe  in 
1815,  and  the  close  of  the  Fratco-Prussian  war  in  1871,  the 
German  engineers  for  the  most  part  of  these  structui’es 
embraced  the  ideas  put  forth  |n  the  works  of  Montalernbert 
and  Carnot,  adopting  for  thjp  plan  of  their  enceintes  the 
polygonal  system  with  flai^king  caponnieres,  combining 
with  these  numerous  casemates  for  defence,  for  bomb-proof 
shelters,  for  quartering  the  troops  and  preserving  the  muni- 
tions and  other  stores. 

132.  From  what  has  been  published  on  this  subject  by 
the  German  engineers  themselves  and  other  European  writ- 
ers, the  following  appear  tb  be  the  leading  features  upon 
which  these  works  are  based: 

1.  To  occupy  the  principal  assailable  points  of  the  posi- 
tion to  be  fortified  by  works  which  shall  contain  within 
themselves  all  the  resources;for  a vigorous  defence  by  their 
garrisons;  these  works  being  placed  in  reciprocal  defensive 
relations  with  each  other,  but  so  arranged  that  the  fall- 
ing of  one  of  them  into  the  besieger’s  hands  will  neither 
compel  the  loss  of  the  others  nor  the  surrender  of  the 
position. 

2.  To  cover  the  space  to  the  rear  of  these  independent 
works  either  by  a continuous  enceinte,  usually  of  the  poly- 
gonal system,  with  a revetted  scarp  of  sufficient  height  to 
secure  it  from  escalade;  thejparts  of  this  enceinte  being  so 
combined  with  the  independent  works  in  advance  that  all 
the  approaches  of  the  besiegers  upon  each,-  both  d^riug 
the  near  and  distant  defenc^,  shall  be  swept  in  the  most. 


78 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


effective  inaimer  bj  their  tire ; or  else  to  connect  these 
works  bj  long  curtains ; or,  tinallj,  to  employ  them,  as  in  a 
system  of  detached  works^  either  to  occupy  important  points 
in  advance  of  the  main/  work,  or  for  forming  capacious 
intrenched  camps  with/  a view  to  the  eventualities  of  a 
war. 

3,  To  provide  the  njost  ample  means  for  an  active  defence 
by  covered- ways  strongly  organized  with  casemated  redoubts, 
and  with  spacious  communications  between  them  and  the 
interior  for  sorties  in  large  bodies. 

4.  So  to  organize  the  artillery  for  the  near  defence  that 
it  shall  be  superior*  to  that  of  the  besiegers  at  the  same 
epoch,  and  be  placed  in  positions  where  it  will  be  sheltered 
from  the  besieger’s  guns  up  to  the  time  tlmt  it  is  to  be 
brought  into  play. 

133.  The  plap  of  the  independent  works  may  be  of  any 
polygonal  figure  which  is  best  adapted  to  the  part  assigned 
them  in  the  defence  of  the  position  ; but  they  are  generally 
in  the  form  off  lunettes,  (PI.  15,  Fig.  2,)  having  a revetted 
scarp  and  counterscarp  to  secure  them  from  escalade. 

In  the  gorgo  of  the  work  a casemated  defensive  barrack 
is  placed,  whidb  serves  as  a reduit  or  keep ; a simple  loop- 
holed  w^all  which  is  flanked  by  the  barrack  closing  the  space 
between  it  apd  the  flanks  of  the  work,  and  securing  the 
latter  from  aij  assault  in  the  rear.  The  ditches  of  the  work 
are  either  fla|iked  from  the  enceinte  in  the  rear ; or,  when 
the  work  is  a| detached  one,  by  caponnieres,  or  counterscarp 
galleries.  The  work  is  usually  organized  with  a covered- 
way having  (|ne  or  more  casemated  redoubts,  and  a system 
of  mines  both  for  the  exterior  and  interior  defence. 

134.  The  ^defensive  barrack  is  usually  arranged  for  two 
or  three  tier^  of  covered  tire,  and  an  upper  one  with  an 
ordinary  parapet  and  terre-plein  on  which  the  guns  are 
uncovered  and  destined  for  the  distant  defence.  The  two 
upper  tiers  o^  covered  tire  are  for  artillery,  to  sweep  the 
interior  of  tpe  work,  and  to  reach  by  curvated  tires  the 
approaches  on  the  exterior.  The  lower  tier  is  loop-holed 
for  musketry  to  sweep  the  interior.  The  barrack  is  sur- 
rounded by  a narrow  ditch  on  the  interior,  and  this,  when 
necessary,  is  flunked  by  small  caponnieres  placed  in  it,  which 
are  entered  from  the  lowest  story.  The  barrack  communi- 
cat(is  with  the  interior  by  a door  at  some  suitable  point ; and 
the  communication  between  the  interior  of  the  work  and  the 
.exterior  is  through  doors  in  the  wall  enclosing  the  gorge. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


79 


135.  Considerable  diversity  is  shown  in  the  profiles  of 
these  works.  They  usually  consist  of  a parapet  and  rampart 
of  ordinary  dimensions  for  the  uncovered  defence  ; of  scarps 
either  partly  detached  and  loop-holed,  with  a corridor 
between  them  and  the  parapet ; or  of  scarps  with  relieving 
arches  arranged  with  loop-holes  for  musketry ; or  of  a com- 
bination of  these  two.  The  height  of  the  barrack,  and  the 
command  of  the  parapet  of  the  exterior  work,  are  so  deter- 
mined that  the  masonry  of  the  former  shall  be  perfectly 
covered  from  the  direct  fire  of  artillery,  and  the  exterior  be 
perfectly  swept  by  the  artillery  of  the  work.  The  portions 
of  the  counterscarps  at  the  salients  are  also  arranged  with 
defensive  galleries  to  sweep  the  ditches ; usually  with  mus- 
ketry, but  in  some  cases  with  artillery. 

136.  Casemates  are  arranged  for  mortars  in  the  salient 
angles  of  the  w’ork,  to  fire  in  the  direction  of  the  capitals  ; 
and  one  or  more  casemated  traverses  are  placed  on  the  terre- 
plein,  to  obtain  a fire  on  the  exterior  and  to  cover  the  terre- 
plein  from  ricochet.  'The  masonry  of  these  traverses  is 
masked  by  the  parapet. 

137.  Posterns  lead  from  the  interior  of  the  work  to  the 
scarp  galleries,  the  corridors,  the  ditch  caponnieres,  and  the 
casemated  moi’tar  battery  in  the  salient. 

138.  The  system  of  mines  for  the  exterior  defence  consists 
simply  of  listening  galleries  leading  outwards  from  the  coun- 
terscarp galleries.  That  for  interior  defence  is  similarly 
arranged;  the  communications  with  it  being  either  from 
the  barrack  caponnieres,  or  from  the  counterscarp  of  its 
ditch. 

139.  The  work  is  provided  with  powder  magazines  which 
are  placed  at  the  points  of  the  interior  least  exposed  to  the 
enemy’s  fire ; and  covered  guard-rooms,  store-rooms  for 
mining  tools,  etc.,  are  made  in  connection  with  the  posterns. 

140.  In  the  profiles  of  their  Works,  the  German  engineers 
follow  nearly  the  same  rules  for,  the  forms  and  dimensions 
of  their  parapets  as  those  in  general  use  in  other  services. 
They  employ  three  kinds  of  scarp  revetments. 

1.  The  ordinary  full  revetment,  or  sustaining  wall,  with 
counterforts. 

2.  Revetments  with  relieving  arqhes,  either  with  or  with- 
out defensive  dispositions,  as  circumstances  may  demand. 

3.  Scarp  walls  either  partly  or  wholly  detached  from  the 
rampart  and  parapet. 

In  all  these  cases,  they  give  to  their  scarp  walls  a height 


80 


ELEMENTS  OF  PERMANENT  FORTIFICATION 


from  27  to  30  feet  for  important  works ; and  about  15  feet 
for  those  less  so.  The  batter  of  these  walls  is  usually  one 
base  to  twelve  perpendicular.  For  the  full  revetment  with 
counterforts,  they  regulate  the  dimensions  of  both  so  as  to 
afford  the  same  stability  as  in  the  revetments  of  Yauban. 

In  their  revetments  with  simple  relieving  arches,  they 
use  either  one  or  two  tiers  of  arches;  placing  the  single  tiei\ 
either  near  the  top,  or  towards  the  middle  of  the  wall, 
according  to  the  nature  of  the  soil  and  the  pressure  to  be 
sustained. 

Revetments  with  relieving  arches  for  defence,  or  scarp 
galleries,  are  arranged  for  one  or  two  tiers  of  tire.  The 
back  of  the  gallery  is  sometimes  left  open,  the  earth  falling 
in  the  natural  slope  in  the  rear;  or  it  is  enclosed  either  with 
a plane  or  a cylindrical  wall,  according  to  the  pressure  to  be 
sustained. 

When  the  upper  part  of  the  wall  is  detached,  to  form  a 
corridor  between  it  and  the  parapet  in  its  rear,  the  top  por- 
tion alone  is,  in  some  cases,  arranged  with  loop-holes  and 
arcades,  or  with  recesses  to  their  rear,  to  cover  the  men 
from  shells;  in  others,  a scarp  gallery  is  made  below  the 
floor  of  the  corridor  to  give  two  tiers  of  fire.  The  corridors 
are  from  8 to  20  feet  in  width  ; and  when  deemed  requisite, 
they  are  divided,  from  distance  to  distance,  by  transverse 
loop-holed  traverse  walls  for  defence. 

When  the  scarp  walls  are  entirely  detached,  they  are 
arranged  for  either  one  or  two  tiers  of  fire,  with  arcades  to 
cover  the  men  ; the  banquette  tread  of  the  upper  tier  of  loop- 
holes resting  on  the  arches  of  the  lower  tier  of  arcades. 

The  counterscarps  are  revetted  either  with  the  ordinary 
wall,  or  arranged  with  a defensive  gallery  with  a full  centre 
arch,  parallel  to  the  face  of  the  counterscarp  wall. 

141.  The  German  engineers  make  a liberal  use  of  bomb- 
proof casemates  for  mortar  and  gun  batteries.  The  former 
are  either  placed  in  the  rear  of  the  parapet,  or  of  the  ram- 
part and  along  the  faces;  or  else  in  a salient  angle. 

In  the  former  case,  they  are  covered  in  front  by  the  para- 
pet; in  the  latter,  either  by  the  scarp  wall  alone,  or  by  a 
casemated  defensive  mask,  placed  in  front  of  the  battery. 

When  placed  along  the  face  (PI.  6,  Fig.  50),  they  are 
arranged  for  one  or  several  mortars,  and  frequently  witli 
two  tiers  of  arches,  the  upper  one  for  the  service  of  the 
mortar,  and  the  lower  one  for  a bomb-proof  shelter  for 
troops,  or  munitions.  The  chamber  occupied  by  each  mor- 
tar is  a rectangle  12  feet  wide  and  about  20  feet  in  depth ; 


ELEMENTS  OF  PERMANE^nT  FORTIFICATION.  81 

this  is  covered  by  a full  centre /rampant  arch,  the  height  of 
the  piers  at  the  back  of  the  (?harnber  being  4 feet  and  in 
front  from  6 to  9 feet  above  fhe  level  of  tlie  mortar-plat- 
form. This  enables  the  shell  to  clear  the  top  of  the  para- 
pet in  front,  which  is  about  ^2  feet  above  the  level  of  the 
platform,  and  21  feet  in  front  of  the  battery. 

The  chamber  is,  in  some  pases,  left  open  both  in  front 
and  rear,  to  allow  the  smojke  to  escape  readily,  and  to 
diminish  the  effect  of  the  concussion  of  the  discharge  on 
the  masonry  ; in  other  cases  it  is  closed  by  a wall  in  the 
rear ; an  opening  being  left  in  this  wall  immediately  under 
the  arch  for  the  same  purpose. 

A small  ditch  is  placed  in  front  of  the  battery ; and  the 
wall  in  front  is  extended  about  three  feet  above  the  plat- 
form, to  shelter  the  men  from  the  explosion  of  shells  that 
may  fall  into  the  ditch. 

The  abutments  of  the  arches  are  7 feet  thick  and  the  piers 
4 feet.  The  arches  are  two  feet  6 inches  thick ; they  are 
covered  on  top  by  from  4 to  6 feet  in  thickness  of  earth  ; 
and,  in  like  manner,  the  arch  and  abutment  are  secured  on 
the  side  exposed  to  an  enfilading  fire. 

An  ordinary  traverse  is  placed  on  the  same  side,  to  cover 
the  masonry  and  communication  between  the  front  of  the 
battery  and  the  parapet ; the  chambers  of  the  mortars  are 
entered  from  the  front,  or  from  the  sheltered  side,  by  a 
door  in  the  abutment. 

When  placed  in  an  obtuse  salient,  behind  a scarp  with  a 
corridor,  a space  of  10  or  12  feet  is  left  between  the  back  of 
the  scarp  wall  and  the  front  of  the  battery.  The  platforms 
of  the  mortars  are  about  the  same  distance  below  the  top 
of  the  scarp.  The  arches  are  covered  by  the  earth  of  the 
parapet  to  the  depth  of  5 or  6 feet.  The  dimensions  and 
arrangement  of  the  chambers  and  arches  are  the  same  in 
this  as  in  the  preceding  case. 

The  communication  from  the  interior  of  the  work  to  the 
battery  is  by  a postern  6 feet  in  width.  A casern ated 
guard-room  is  made  in  connection  with  the  postern  ; and 
when  the  scarp  is  arranged  with  relieving  arches,  either  for 
defence  or  for  other  purposes,  an  arched  stairway  is  in  some 
cases  made  as  a communication  from  the  postern  to  the 
casemates.  A transversal  wall  with  a doorway  serves  to  cut 
off  the  court  in  front  of  the  battery  from  the  corridor  to 
the  rear  of  the  wall. 

In  the  less  obtuse  salients,  the  front  of  the  battery  is 


82 


ELEMENTS  OE  PERMANENT  FORTIFICATION. 


made  circular ; the  chambers  beiug  so  placed  that  the  fire 
of  the  mortars  can  be  thrown  in  the  direction  of  the  capital. 
A casemated  defensive  traverse,  placed  in  the  salient,  masks 
the  battery  in  front ; and  it  is  covered  on  the  flanks  by  the 
earth  on  the  top  of  the  arches.  The  details  otherwise  are 
the  same  as  in  the  preceding  case. 

142.  In  the  arrangement  of  casemated  traverses  for 
guns  (PI.  6,  Figs.  48,  49),  the  chamber  for  each  gun  is  a 
rectangle  24  feet  in  depth,  estimated  from  the  interior  crest 
of  the  parapet,  and  12  feet  wide.  The  chamber  is  covered 
by  a full  centre  arch,  the  height  from  the  level  of  the  plat- 
form to  the  crown  of  the  arch  being  8^  feet.  The  arch  is 
2 feet  thick,  the  piers  between  the  arches  3 feet,  and  the 
abutments  3^  feet.  The  mask  wall  in  front  of  the  cham- 
bers is  3 feet  thick.  This  wall  is  covered  in  front  by  the 
parapet,  and  by  several  layers  of  fascines,  or  of  heavy  tim- 
ber laid  across  the  embrasure  in  the  parapet  and  above  the 
one  through  the  mask  wall.  The  cheeks  of  the  embrasure 
in  the  parapet  are  likewise  revetted  with  heavy  timber  at 
some  distance  in  front  of  the  mask  wall.  The  masonry  is 
covered  on  top  and  on  the  sides  with  5 or  6 feet  thickness 
of  earth,  to  secure  it  from  shells  and  enfilading  shot.  The 
casemates  are  left  open  to  the  rear. 

In  some  cases,  a blinded  battery  for  a single  gun  (PI.  6, 
Fig.  49),  is  arranged  by  enclosing  the  sides  and  front  of  the 
chamber  with  walls,  and  covering  it  with  a layer  of  heavy 
timber,  supporting  two  thicknesses  of  large  fascines,  cov- 
ered with  a thickness  of  5 or  6 feet  of  earth  ; the  dimensions 
of  the  chamber  are  the  same  as  in  the  preceding  case. 

143.  The  caponnieres  (PI.  5,  Figs.  37,  38),  for  flanking 
the  main  ditch,  usually  consist  of  two  faces  and  two  case- 
mated  flank  batteries  of  two  stories  each ; the  lower  story 
being  loop-holed  tor  musketry,  and  the  upper  pierced  for 
artillery.  Each  battery  consists  of  several  rectangular  cham- 
bers ; each  chamber  for  a single  gun  being  12  feet  wide  and 
24  feet  deep ; or  of  smaller  dimensions,  according  to  the 
calibre  of  the  gun  and  the  kind  of  carriage  on  which  it  is 
mounted.  The  upper  chambers  are  covered  wT'i  bomb- 
]U’oof  arches,  the  lower  one  by  arches  of  sufficient  strength 
for  the  weight  thrown  upon  them.  The  front  mask  wall  of 
the  casemates  is  6 feet  thick ; the  wall  in  the  rear  is  3 feet 
thick  and  is  pierced  with  windows  for  light  and  ventilation. 
Openings  for  the  escape  of  the  smoke  are  also  made  in  the 
front  mask  wall  immediately  below  the  crowns  of  the  arches. 


83 


/ 

/ 

/ 

/ 

ELEMENTS  OF  PERMA^NT  FORTIFICATION. 

An  interior  court  30  feet  in  width  is  left  between  the  two 
flank  batteries,  and  when  the  batteries  are  detached  from 
the  scarp  wall  the  space  betv^een  is  enclosed  by  a loop-holed 
wall  built  on  each  side  in  the^  prolongation  of  the  front  mask 
wall. 

The  faces  of  the  caponniere  form  a salient  of  60°.  They 
are  separated  from  the  flanks  by  two  stories  of  arched  corri- 
dors, in  front  of  which  are  two  arched  chambers  of  two 
stories ; the  upper  chamber  being  arranged  for  mortars. 
An  open  triangular  court  is  left  between  the  front  walls  of 
these  chambers  and  the  faces  of  the  caponniere.  The  upper 
part  of  the  walls  of  the  faces  along  this  court  are  arranged 
with  arcades  and  loop-holed  for  musketry,  and  have  an  open 
corridor  in  their  rear  on  the  same  level  as  the  chambers  of 
the  second  story. 

The  caponniere  is  provided  with  a powder  magazine  and 
other  necessary  conveniencies  for  the  defence. 

The  flanks  of  the  caponniere  and  its  interior  are  swept  by 
the  musketry  of  the  scarp  galleries  in  its  rear.  The  faces 
in  like  manner  are  swept  by  artillery  and  musketry  in  case- 
mates behind  the  scarp. 

The  arched  chambers  of  the  upper  story  are  covered  by  a 
thickness  of  5 or  6 feet  of  earth. 

144.  Caponnieres  of  smaller  dimensions,  termed  hastion- 
nets  (PI.  5,  Fig.  39),  placed  at  the  angles  of  redoubts  to  flank 
the  ditches,  are  usually  arranged  for  musketry,  but  some- 
times receive  artillery.  Those  for  flanking  the  ditches  of 
the  independent  works  in  advance  of  the  enceinte,  are  some- 
times placed  in  the  ditches  of  these  works  ; sometimes  be- 
hind the  scarp  wall  of  the  enceinte ; and  sometimes  in  case- 
mates in  the  main  ditch,  detached  from  the  scarp  wall. 

The  communications  from  the  interior  with  the  capon- 
niewes  are  by  posterns. 

145.  The  defensive  barracks,  forms  one  of  the  most  dis- 
tinctive features  in  the  organization  of  the  German  fortifl- 
cationSo  The  plan  of  these  works  may  be  of  any  figure  to 
suit  the  object  to  be  subserved  by  them.  Wlien  placed  in 
the  gorge  of  an  independent  work  and  serving  as  a keep  to 
it,  their  plan  is  usually  semicircular.  (PI.  15,  Fig.  2.) 

The  barrack  consists  of  one  or  two  stories  of  arched 
chambers  for  covered  fire,  and  an  open  battery  on  top  with 
an  earthen  parapet  and  terre-plein. 

The  arched  chambers  are  formed  by  connecting  the  front 
and  rear  walls  of  the  barrack  by  transversal  walls  which 


84 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


serve  as  piers  for  the  arches  of  the  ceiling,  the  soffits  of 
which  are  either  cylindrical  or  conoidal,  according  as  the 
piers  are  parallel  or  otherwise.  The  chambers  are  about  18 
to  20  feet  wide,  and  60  feet  in  depth ; their  height,  under 
the  crown  of  the  arch,  from  9 to  11  feet.  The  arch  of  the 
highest  chamber  is  feet  thick,  and  being  covered  with  a 
capping  and  the  earth  of  the  open  battery  on  top,  is  bomb- 
proof. The  arches  of  the  lower  stories  are  1^  feet  thick. 
The  front  wall  of  the  barrack  is  usually  6 feet,  and  is  pierced 
in  each  chamber  with  one  embrasure  and  two  loop-holes. 
The  rear  wall  is  3 feet  thick,  and  has  a window  in  each 
chamber  for  light  and  ventilation.  Openings  for  ventilation 
are  also  made  in  the  front  wall  just  beneath  the  crowns  of 
the  arches.  Doorways  are  made  through  the  transversal 
walls  to  form  a communication  between  all  the  chambers. 
These  are  sometimes  placed  along  the  centre  of  the  piers,  at 
others  near  their  extremities,  so  that  the  chambers  being 
divided  by  slight  partitions  into  two  compartments  for  the 
quartering  of  the  troops,  there  will  be  a continuous  hall 
either  along  the  centre,  or  near  the  rear  wall,  upon  which 
all  the  apartments  open.  The  barracks  are,  otherwise, 
arranged  with  all  the  requisites  for  lodging  the  troops  com-^ 
fortably  and  healthfully.  The  lower  story  of  the  barrack  i& 
surrounded  by  a narrow  ditch.  A drawbridge  across  this 
ditch  secures  the  entrance  to  the  barrack  at  the  gorge. 

In  some  cases  where  the  front  wall  of  the  barrack  is  much 
exposed  to  the  besieger’s  hre,  the  piers  are  made  thicker 
nearer  the  front  wall ; and  they  each  have  two  vertical 
grooves  to  receive  timber,  laid  horizontally,  between  which 
sand-bags  can  be  packed  in  to  afford  shelter  when  the  front 
wall  has  become  much  damaged  by  the  besieger’s  artillery. 

146.  Remarks.  The  foregoing  summary  description,, 
with  the  plates,  will  give  a good  general  idea  of  the  princi- 
pal defensive  arrangements  constructed  of  masonry  which 
enter  so  largely  into  the  existing  German  fortifications,  and 
upon  the  details  of  which  the  German  engineers  have  be- 
stowed great  attention. 

The  adoption  of  the  polygonal  system,  with  caponniere 
defences  for  the  main  ditch,  has  enabled  the  German  engi- 
neers to  give,  in  their  fortifications,  a greater  exterior  side 
than  in  the  bastioned  system  generalljq  and  still  admit  of 
lines  of  defence,  in  which  grape,  canister  and  small-arms, 
particularly  the  later  improved  musket,  will  tell  with  effi- 
cacy upon  the  besieger’s  works  on  the  glacis  around  the 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


85 


salients  of  the  enceinte.  With  a few  exceptions,  nothing  of 
a very  reliable  character  has  been  published  as  to  the  plan 
of  these  works,  further  than  the  general  defensive  disposi- 
tions. From  these  it  appears  that,  keeping  in  view  the 
cardinal  point  in  all  fortification,  the  adaptation  of  the  vari- 
ous fronts  to  the  site  of  the  work,  so  that  all  the  approaches 
upon  them  shall  be  commanded  and  swept  by  their  fires, 
whilst  the  principal  lines  of  the  enceinte  receive  the  best 
direction  to  place  them  as  little  as  possible  within  the  range 
of  enfilading  positions,  the  exterior  side  is  usually  kept 
somewhere  between  500  and  600  French  metres,  or  between 
550  and  YOO  yards. 

147.  This  system  of  fortifications  being  in  existence 
before  the  recent  improvements  in  arms  and  the  works 
being  located  in  accordance  with  correct  principles,  the 
changes  required  in  them  are  of  detail  and  dimensions 
rather  than  of  principle.  The  principal  changes  of  a gen- 
eral character  are : 1st,  in  reducing  the  number  of  strong 
places,  retaining  those  guarding  the  frontier,  and  those 
covering  strategic  points,  large  depots  of  supplies  and  cen- 
tres of  production.  These  include  generally  centres  of  com- 
munication and  some  of  the  large  cities.  2d,  in  enlarging 
the  detached  forts,  placing  them  further  from  the  centre  of 
defence  (from  4 to  8 miles)  and  making  them  much  stronger, 
placing  in  the  intervals  between  them,  when  necessary, 
smaller  redoubts  or  batteries,  thus  making  an  exterior  line 
of  defence  of  great  development  and  within  which  large 
armies  can  be  assembled  and  manoeuvred. 

The  existing  enceintes  enclosing  cities  thus  fortified  will 
in  general  be  retained,  or,  as  at  Cologne,  replaced  by  a con- 
tinuous enclosure,  without  outworks,  generally  polygonal, 
with  flanking  bastionettes,  provided  with  revetted  scarps  and 
<30unterscarps ; the  parapet  being  arranged  for  infantry,  and 
field  or  garrison  guns  of  moderate  calibre,  the  whole  being 
•designed  for  security  against  attack  or  escalade  by  any  force 
breaking  through  the  outer  lines,  but  owing  to  its  prox- 
imity to  the  city  not  intended  to  withstand  regular  ap- 
proaches. 

The  detached  works  already  built  may  be  used  as  a second 
line,  or  in  many  cases  destroyed. 

The  fortifications  of  those  cities  which  are  not  strength- 
ened, and  the  small  forts  not  included  in  the  classes  named, 
may  be  either  retained  unaltered  or  torn  down. 


The  principal  changes  required  in  the  details  of  the  works 
described  in  order  to  fit  them  for  defence  are  as  follows,  viz. : 


86 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


The  covered-wajs  should  be  reduced  in  width,  to  draw 
their  crests  nearer  the  scarp  wall.  The  defensive  barracks, 
keeps,  bastionettes,  and  caponnieres,  should  be  cut  down  to 
one  tier  of  tire,  their  face-walls  masked  and  their  arches 
covered  with  a sufficient  thickness  of  earth  to  render  them 
bomb-proof.  All  casemates  exposed  to  direct  tire  must  be 
thoroughly  masked  or  shielded  with  armor. 

The  scarp  walls  may  be  reduced  to  a height  of  from  13 
to  23  feet,  according  to  the  importance  of  the  work,  and 
covered  against  a plunging  tire  by  the  glacis.  Wing  bat- 
teries for  tianking  and  ditch  defence  may  be  built  outside 
the  work  in  the  continuation  of  the  gorge,  and  other  changes 
made  to  bring  them  so  far  as  practicable  into  conformity 
with  the  most  recent  constructions. 

II. 

FRONTS  OF  POSEN. 

148.  The  following  is  an  outline  of  the  plan  and  de- 
fensive dispositions  of  a front  of  the  fortitications  of  Posen, 
one  of  the  most  noted  of  these  structures. 

The  exterior  side,  ab,  (PI.  14,  Fig.  2),  is  600  yards ; a 
distance,  cd  = yig-  ab,  is  set  off  on  the  perpendicular  to  the 
front  and  without  it ; and  on  the  line  joining  the  salients  a, 
B with  D,  distances,  ah,  bm,  equal  ^ ab,  being  set  off,  give 
the  faces  of  the  front. 

The  salient,  e,  of  the  independent  work  is  on  the  per- 
pendicular of  the  front,  and  at  a distance  from  c equal  to  |- 
AB.  Describing  from  e an  arc  with  a radius  of  20  yards, 
and  drawing  tangents  to  it  from  the  points  h and  m,  gives 
the  counterscarps  of  the  independent  work  ; the  faces,  ef^ 
ef',  are  parallel  to  the  counterscarp  and  equal  ^ ab. 

The  ditches  of  this  work  are  tianked  by  casemated  capon- 
nieres, HI,  MN,  which  are  35  yards  in  length,  or  sufficient 
for  four  guns  ; the  directions  of  these  tianking  casemates 
being  nearly  perpendicular  to  the  direction  of  the  faces  ef'. 
The  flanks,  fg,  f'g',  receive  the  most  suitable  directions  for 
sweeping  the  approaches  in  advance  of  the  salients  of  the 
front. 

The  main  ditch  is  about  30  yards  wide,  its  counterscarp 
being  parallel  to  the  faces  of  the  enceinte;  and  the  gorge 
of  the  independent  work  is  on  the  prolongation  of  this 
counterscarp. 

The  curtains  of  the  enceinte  are  directed  from  the  points 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


87 


T,  N on  the  point  c,  and  are  thtis  nearly  parallel  to  the  ex- 
terior side. 

The  main  ditch  is  flanked  a large,  casemated,  defensive 
barrack,  having  three  stories  of  covered  Are,  the  lower  for 
musketry  and  the  upper  for  ^rtillery,  and  an  open  battery 
on  top.  The  plan  of  this  work  is  that  of  the  letter  u ; the 
circular  part  projects  withip  the  independent  work,  and  * 
serves  as  its  keep ; the  sides  are  nearly  perpendicular  to  the 
faces  of  the  enceinte,  and  ar^  prolonged  within  the  enceinte, 
serving  as  a defensive  capopniere  to  flank  the  main  ditch, 
to  sweep  the  terre-pleins  of  the  enceinte  curtains,  and  also 
the  interior  within  the  ranhe  of  the  guns  of  two  round 
towers  with  which  the  sides!  are  terminated.  The  sides  of 
the  barrack  are  separated  from  the  rampart  of  the  curtain  by 
lateral  ditches  10  yards  wid^,  which  give  access  to  the  main 
ditch  from  the  interior  for  troops  in  large  bodies  for  sorties. 

The  parapet  of  the  enceinte  (Fig.  4)  is  thrown  back  from 
the  scarp,  leaving  a corridor  between  the  foot  of  its  ex- 
terior slope  and  the  scarp  w^ll,  the  floor  of  w^hich  is  12  feet 
above  the  bottom  of  the  main  ditch. 

The  scarp  wall  rises  16  feet  above  the  level  of  the  floor, 
thus  giving  it  a total  height  of  28  feet  above  the  bottom  of 
the  main  ditch.  This  wall  is  loop-holed  for  small  arms. 

The  counterscarp  wall  of  The  main  ditch  is  24  feet  in 
height.  ; 

The  faces  and  flanks  of  the  enceinte  have  a relief  of  44 
feet ; the  relief  of  the  curtain  being  only  40  feet. 

The  corridors  of  the  curtain  terminate  at  the  court  or 
open  space  behind  the  flanking  casemates,  hi,  mn. 

Posterns  lead  from  the  iiiterior  to  the  corridors  of  the 
faces  and  flanks,  and  from  the  lateral  ditches  to  the  cor- 
ridors of  the  curtain.  i 

The  interior  open  space  between  the  sides  of  the  de- 
fensive barrack  is  closed  by  ^ loop-holed  wall  between  the 
end  towers.  A ditch  surroupds  the  towers  and  the  gorge 
between  them,  across  which  a;  bridge,  terminated  at  the  wall 
by  a draw,  gives  access  to  thp  interior  open  space  and  the 
barracks.  i 

149.  The  scarp,  rampart  pnd  parapet  (Fig.  5),  of  the 
independent  work  are  arranged  with  a profile  similar  to  tliat 
of  the  enceinte.  The  circular  portion  of  the  defensive  bar- 
rack which  serves  as  the  keep  is  surrounded  by  a ditch, 
which  is  swept  by  small  caponnieres  attached  to  the  keep. 
A circular  mortar  battery,  covered  in  front  by  a casemated 
traverse,  is  placed  in  the  angle  of  the  independent  work 


88 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


and  behind  this  a casemated  battery  for  howitzers  is  placed 
on  its  terre-plein,  in  the  direction  of  its  capital,  to  give  reverse 
lire  on  the  glacis  of  the  collateral  independent  works.  The 
gorire  of  this  work  is  closed  by  a loop-holed  wall  which  ex- 
tends between  the  keep  and  the  scarp  wall  of  the  flanks. 

The  communication  between  the  main  ditch  and  the  in- 
terior is  through  a gateway  in  this  wall.  Posterns  lead 
from  the  interior  to  the  corridors  of  the  faces  and  flanks, 
and  to  the  mortar  battery  in  the  salient. 

150.  The  counterscarp  of  the  independent  work  is  ar- 
ranged with  a defensive  gallery,  with  which  a system  of 
mines  for  the  exterior  defence  is  connected.  An  interior 
system  of  mines  is  connected  with  the  small  caponuieres  in 
the  ditch  of  the  keep. 

151.  The  covered- way  is  without  the  usual  traverses,  its 
interior  crest  being  broken  into  a cremailliere  line.  Its 
salient  and  reentering  places-of-arms  are  occupied  by  case- 
mated  redoubts.  The  communications  from  the  main  ditch 
to  the  covered-way  are  by  wide  ramps  which  are  at  the 
gorges  of  the  reentering  places-of-arms  and  under  the  fire 
of  their  redoubts. 

III. 

FORT  ALEXANDER. 

Among  the  most  reliable  of  the  published  plans  of  Ger- 
man fortification  is  that  of  the  main  front  of  Fort  Alexander, 
a detached  quadrilateral  work  of  the  fortifications  of  Cob- 
lentz,  given  by  Colonel  Humphrey  of  the  British  Army. 

152.  Plan.  The  exterior  sides  of  the  enceinte  of  this 
fort  (PI.  14,  Fig.  6)  form  a parallelogram,  the  acute  angles 
of  which  are  85°.  The  main  and  rear  fronts  are  each  .500 
yards,  and  the  other  two  420  yards  each.  The  main  front 
is  of  the  polygonal  system,  with  a strong  defensive  capon- 
niere  to  flank  the  main  ditch. 

The  caponniere  is  covered  by  a demi-lune,  and  the  salients 
of  the  enceinte  by  counterguards  ; the  ditches  of  these 
works  being  flanked  by  casemated  batteries  at  the  reenter- 
ing formed  between  them. 

There  is  no  covered-way  in  front  of  these  outworks,  their 
counterscarps  being  of  earth  with  a gentle  slope.  A small 
earthen  work,  containing  a casemated  redoubt,  is  thrown  up 
at  the  salients  of  the  counterguard  counterscarp. 

To  construct  the  trace,  take  ab  = 500  yards  for  the  ex- 
terior side  of  the  enceinte,  which  divide  into  three  equal 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


89 


parts,  ad  = de  = eb.  Bisect  ab  by  a perpendicular  on  which 
set  off  hn  hd  = he  = ^ ab.  Tm’ongh  h drawing  a paral- 
lel to  ab  and  setting  off  along  it  the  distances  ha  = hb  = 
320  yards,  the  points  a and  b will  be  the  salients  of  the 
counterguards. 

From  H,  as  a centre,  with  the  radii  nd  = ne,  describe  two 
arcs,  on  which  set  off  from  d and  e the  chords  di  = ek  = 33 
yards,  these  will  be  the  lengths  of  the  casemated  ffanks ; ik 
being  joined  gives  the  enceinte 'curtain. 

The  salient  angle  of  the  majn  caponniere  is  constructed 
by  drawing  from  a point,  m,  on  the  capital,  at  a distance  of 
20  yards  from  the  lines  nd.  He,  lines  to  the  extremities  i and 
k of  the  casemated  flanks.  The  flanks  of  the  caponniere, 
tn  = VO,  extend  back  to  the  exterior  side,  and  are  33  yards 
in  length  and  33  yards  apart;  or  each  16^  yards  on  ©ach 
side  of  the  capital. 

The  faces  of  the  counterguards  are  directed  on  the  point 
c = AB  = 53^  yards  on  the  capital  from  h. 

The  salient  f,  of  the  demi-lune  is  ab  = 106  yards  from 
the  point  c;  its  faces  fd,  fe,  are  parallel  to  the  lines  Hd,iie, 
which  last,  joined  by  an  arc  of  a circle  described  from  m as 
a centre,  with  a radius  of  20  yards,  and  terminated  at  the 
counterscarp  of  the  enceinte  ditch,  which  is  28  yards  from 
ab,  will  give  the  demi-lune  gorge. 

A casemated  battery  for  3 guns,  behind  the  demi-lune 
■scarp  wall,  flanks  the  counterguard  ditch ; and  one  for  3 
guns  flanks  the  demi-lune  ditch,  and  closes  the  opening  be- 
tween the  demi-lune  and  counterguard  at  this  point.  A 
narrow  ditch  10  feet  wide  is  left  between  the  flank  of  this 
battery  and  the  extremity  of  the  counterguard,  as  a commu- 
nication between  the  main  ditch  and  the  ditches  of  the  out- 
works. This  opening  is  masked  by  an  overlap  of  the  coun- 
terguard. 

Casemated,  or  blinded,  batteries  are  made  in  the  salients 
-of  the  enceinte  and  of  the  demi-lune. 

153.  The  main  caponniere  (Fig.  8)  has  two  tiers  of 
•covered  artillery  fire  on  the  flanks,  of  5 guns  each  ; the 
lower  to  sweep  the  main  ditch,  the  upper  the  terre-pleins  of 
the  counterguards  ; its  faces  have  two  tiers  of  loop-holes.  It 
has  no  uncovered  fire,  but  a simple  covering  of  earth  as  a 
bomb-proof. 

154.  Casemates  for  five  mortars  each,  are  placed  in  the 
salients  of  the  enceinte  at  the  foot  of  the  rampart  slope. 

155.  A narrow  corridor  (Fig.  7),  the  floor  of  which  is  4^ 
feet  above  the  bottom  of  the  main  ditch,  is  left  behind  the 


90 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


scarp  wall  of  the  enceinte ; the  faces  and  curtains  of  this- 
wall  are  loop-holed  and  arranged  with  arcades  to  shelter  the 
men,  like  the  detached  scarp  walls  of  Carnot.  These  scarps 
are  21  feet  high.  The  height  of  the  enceinte  above  the 
parade  is  26  feet. 

156.  The  scarp  walls  of  the  demi-luneand  counterguards 
(Fig.  T,)  are  arranged  like  those  of  the  enceinte.  The  com- 
mand of  these  works  is  16  feet.  Their  counterscarps  are 
arranged  at  the  salients  with  loop-holed  galleries,  from 
which  communications  lead  to  a system  of  mines  for  ex- 
terior and  interior  defence. 

157.  The  rear  side  of  this  fort,  not  being  exposed  t0‘ 
artillery,  is  simply  closed  by  a lo^-holed  wall  and  ditch.  A 
large,  circular,  defensive  barrack  occupies  the  centre  of  this- 
rear  front,  serving  as  a keep  tojthe  fort,  and  to  sweep  by  its 
fire  the  ground  on  the  rear  and  flanks  of  the  front. 

158.  Up  to  1883  no  changes  had  been  made  in  this  or 
the  other  works  about  Cobmntz,  but  additional  detached 
works  had  been  built  further  from  the  city. 

159.  Remarks.  It  will  me  seen  that  in  the  arrangement 
of  the  plan  of  this  work,  ttfe  polygonal  system,  with  capon- 
niere  defences,  of  Montaldmbert,  has  been  adopted  as  the 
basis,  with  such  modific^ions  as  the  features  of  the  site 
afforded  to  withdraw  the  principal  lines  from  the  range  of 
enfilading  views. 

The  German  engineer!  apply  the  preceding  dispositions^ 
to  every  class  of  detach efl  works,  whether  within  reach  of 
the  artillery  of  the  main  work  or  beyond  it. 

In  the  former  case  tl  e work  is  either  in  the  form  of  a 
lunette  or  a redan,  according  to  the  requirements  of  the 
site ; the  gorge  of  the  work  being  secured  by  a slight  loop- 
holed  wall  that  can  be  ; ‘eadily  destroyed  by  the  artillery  of 
the  place  ; and  thus  ope  i its  interior  to  view  when  occupied 
by  the  besieger. 

In  the  latter,  the  pla  i is  that  of  polygonal  redoubt  en- 
closed on  all  sides  by  a ] arapet. 

The  ditches  in  all  sue  i cases  are  flanked  by  small  capon- 
nieres,  placed  at  the  angfes  of  the  work,  and  arranged  both, 
for  musketry  and  artilleiw ; besides  having  a counterscarp 
gallery  which  serves  as  tfte  point  of  departure  for  the  gal- 
leries of  the  exterior  system  of  mines. 

The  apparently  wide  ivergence  between  the  German- 
fortification  of  the  present  day  and  the  bastioned  system, 
which  last  had  been  adopt^  as  the  normal  one  throughout 
the  world  until  these  innoyations  were  practically  intror 


ELEMENTS  OF  PEEMANE^  FORTIFICATION.  91 

/ 

duced,  lias  given  rise  to  active/discnssions  among  engineers 
in  Europe,  in  which,  as  in  arf  cases,  very  ultra  ground  has 
been  taken  by  both  parties  \p  the  dispute. 

160.  In  each  system  thd  points  admitted  as  essential  in 

all  fortification  of  a perr/anent  character  are  sought  for, 
viz. : / 

1.  An  enceinte  secup  from  escalade  and  thoroughly 
fianked  by  artillery  and/small-arms. 

2.  Such  an  adaptati^  of  the  plan  of  the  enceinte  to  the 
site  as  shall  secure,  as  ftar  as  practicable,  the  principal  lines 
from  enfilading  view* 

3.  Outworks  and  aetached  works  oi  sufficient  strength  in 
themselves,  and  of  such  defensive  relations  to  the  enceinte, 
as  to  force  the  besi^er  to  carry  them  by  regular  approaches 
before  being  able  tp  assault  the  enceinte. 

4.  Interior  defensive  works,  or  keeps  within  the  assail- 
able points  of  the/ enceinte  ; and  also  in  the  outworks  first 
subject  to  an  attadk,  to  give  confidence  to  their  garrisons  in 
holding  out  to  the  last  extremity. 

5.  The  means  pecessary  for  an  active  defence. 

6.  The  use  of  ixiines  as  an  auxiliary. 

7.  The  protection  of  all  masonry  by  earthen  masks  from 
the  distant  batt^ies  of  the  besieger. 

The  only  question  then  is  by  which  of  these  two  systems 
the  object  in  vifew  is  best  attained. 

161.  The  polygonal  trace  which  obtains  in  most  of  the 
recent  German  Iworks  has  certain  prominent  advantages  and 
defects  which  itiay  be  seen  by  a slight  comparison  with  the 
bastioned  systeffi. 

As  the  exterfor  sides  are  longer  and  the  reentering  of  the 
enceinte  less  d^ep  than  in  the  bastioned  systems,  it  follows : 

1.  That  the f interior  space  enclosed  by  the  enceinte  is 
greater  in  the  polygonal  trace. 

2.  That  the  j faces  of  the  enceinte  are  less  exposed  to 
ricochet  from  tfie  greater  obtuseness  of  the  salient  angles. 

3.  That  the  fire  of  the  faces  has  thus  a better  bearing  on 
the  distant  defence. 

4.  That,  requiring  fewer  fronts  on  a given  extent  of  line 
to  be  fortified,  there  will  be  fewer  flanks  and  more  artillery 
therefore  disposable  for  the  faces  and  curtains. 

5.  That,  in  the  usual  mode  of  attack,  the  besiegers  will  be 
forced  into  a greater  development  of  trenches  for  the  same 
number  of  fronts. 

162.  Its  defects  are  : 

1.  That  the  enceinte,  having  no  other  flanking  defence 


"92  ELEMENTS  OF  PERMANENT  FORTIFICATION. 

than  the  main  caponniere,  will  be  exposed  to  an  escalade  so 
soon  as  the  fire  of  this  defence  is  silenced. 

2.  That  the  progress  of  the  besiegers  during  the  last  and 
most  important  period  of  the  siege  is  but  little  delayed, 
owing  to  the  slighter  reenterings  tj&med  by  the  independent 
works  in  front  of  the  enceinte  sal/ents. 

163.  The  defects  in  the  bas^oned  trace  and  the  modes 
proposed  by  different  engineers  to  remedy  them,  particu- 
larly those  of  Choumara,  have  jpeen  sufficiently  dwelt  upon 
to  show  that,  with  the  advant^es  inherent  in  this  trace  of 
preserving  the  means  of  flankilig  the  enceinte  ditch  to  the 
last ; of  throwing  the  bastion  palients  into  deep  reenterings ; 
and  giving  a better  direction  |b  the  enceinte  faces  for  sweep- 
ing the  ground  in  advance  off  the  demi-lune  salients;  it  is 
susceptible  of  receiving  all  fthe  means  of  casemated  de- 
fences ; of  a great  developn^nt  of  flank  fire ; of  defensive 
arrangements  of  mines ; oflample  communications  for  an 
active  defence ; and  an  extension  of  the  exterior  side  forti- 
fied commensurate  with  thp  improvements  of  late  years  in 
artillery  and  small-arms.  | 

This  last,  together  withf  a shorter  perpendicular  to  the 
front,  giving  relatively  shorter  flanks,  the  breaking  back  of 
the  parapet  in  the  polygcmal  front  for  flanking  the  capon- 
nieres,  the  introduction  oft  armored  casemates  and  turrets 
for  flanking  the  ditches,  |he  extensive  use  of  covered  de- 
fences, the  simplification  |of  the  outworks  and  reduction  in 
their  command  in  both  sjstems,  have  materially  diminished 
the  marked  points  of  difiperence,  and  have  brought  the  two 
systems  more  nearly  inti  equality  for  both  the  close  and 
distant  defence.  | 

164.  In  the  discussions  which  have  taken  place  upon  the 
merits  of  these  two  traaes,  between  engineers  of  the  two 
rival  schools,  each  has  seemed  disposed  to  exaggerate  the 
defects,  and  to  depreciate  the  advantages  of  the  system 
analyzed,  and  has  conducted  his  mode  of  attack  accordingly. 
The  true  point,  however^  as  to  the  inherent  merits  of  the 
question,  does  not  lie  in  a comparison  of  the  means  of  resist- 
ance of  a bastioned  trace  with  defective  communications  and 
without  casemated  defences  and  mines  with  that  of  the 
German  system,  but  between  the  former  with  these  addi- 
tions, now  regarded  by  engineers  of  every  school  as  indis- 
pensable to  a vigorous  defence  against  the  greatly  improved 
means  of  attack  of  the  present  day,  and  the  latter. 

In  these  discussions  many  considerations  arising  from  the 

1 


/’ 

/ 

,/ 

ELEMENTS  OF  PE|tilANENT  FORTIFICATION.  93- 

y 

immediate  vicinity  of  y4ie  protected  city  to  the  fronts  of 
attack  have  been  introSuced. 

The  great  range  of  modern  guns  has  made  it  impossible 
to  defend  a city  frogi  its  immediate  suburbs,  and  has  led  to 
arranging  for  both/close  and  distant  defence  the  forts  of  the 
belt  or  belts  encii;bling  the  place,  leaving  for  the  enceinte 
only  the  duty  of/protecting  the  city  from  the  attack  of  an 
army  (perhaps  Urge)  which  may  break  through  the  outer 
line.  / 

The  enceinte  to  satisfy  the  conditions  requisite  for  this 
defence  must/be  proof  against  assault  or  escalade,  but  will 
not  require  elaborate  outworks  or  interior  retrenchments. 
The  cheapest  and  simplest  system,  either  polygonal  or 
circular,  or  a combination  of  them,  will  be  in  general 
adopted. 

The  outworks  will  be  restricted  to  those  necessary  to  pro- 
tect the  gates;  the  interior  retrenchments  to  those  required 
to  keep  the  disorderly  element  of  the  inhabitants  in  sub- 
jection. ^ 

For  thfe  detached  works,  subject  to  regular  approaches, 
the  relative  values  of  the  rival  systems  must  be  determined 
by  the  circumstances  of  the  particular  case  to  which  they 
are  to  be  applied. 


94 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


CHAPTER  YI. 

DETACHED  FORTS. 


165.  For  reasons  previously  stated,  tlie  main  line  of  de- 
fence of  fortified  places  is  now  at  the  belt  of  detached  forts 
instead  of  at  the  enceinte.  These  forts  have  acquired  all 
the  additional  value  due  to  this  fact,  and  thejatest  develop- 
ments in  the  art  of  fortification,  for  land  fronts,  are  to  he 
found  in  the  newest  detached  works  of  the  German,  French, 
and  Belgian  engineers. 

166.  These  forts  are  as  a rule  polygonal,  the  traces  gen- 
erally adopted  are  a long  straight  front  with  two  flanks  and 
a gorge,  which  may  be  rectilinear,  tenailled  or  bastioned  ; a 
lunette  with  a very  obtuse  salient ; or  a modification  of  the 
lunette  which  has  three  or  sometimes  four  faces  and  two 
flanks.  The  character  of  the  gorge  is  determined,  in  all 
cases,  by  the  nature  of  the  site  or  the  individual  views  of 
the  designing  engineer. 

The  faces  and  flanks  of  these  forts  which  give  a direct  fire 
to  the  front  have  together  a length  of  from  300  to  700  yards. 
The  depth  of  the  forts  from  front  to  gorgeis  a minimum  con- 
sistent with  sufficient  interior  space  for  the  accommodation 
of  their  garrisons  which  vary  from  500  to  1000  men.  The 
armament  of  the  largest  is  about  30  guns.  Plate  16,  taken 
from  a German  authority,  shows  the  details  of  one  of  these 
works. 

Their  parapets  have  a command  of  from  25  to  40  feet  at 
the  salients  and  fall  ofi  towards  the  flanks  and  gorge  for 
defilade. 

The  faces  and  flanks  receive  a thickness  of  from  20  to  25 
feet  and  the  gorges  about  15  to  18  feet.  The  ditches  have 
a minimum  depth  of  20  and  width  of  30  feet. 

The  scarp  walls  are  generally  detached  or  semi-detached 
and  loopholed  for  defence. 

They  have  such  height,  usually  not  less  than  16  feet,  as 
bo  be  well  protected  by  the  glacis. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


95 


The  counterscarps  are  generally  revetted  with  masonry 
walls  with  relieving  arches,  which  lend  themselves  to  the 
construction  of  counterscarp  galleries  for  sweeping  the 
ditches  and  for  starting  points  for  countermines.  The  faces 
are  flanked  by  artillery,  machine  guns  or  infantry  fire  from 
caponnieres,  and  the  flanks  by  caponnieres  or  scarp  galleries, 
a sheltered  emplacement  for  which  is  obtained  by  breaking 
back  the  scarp  wall  at  the  shoulder  angles  and  forming  a 
kind  of  orillon,  in  the  rear  face  of  which  the  casemates  are 
placed. 

167.  The  interiors  of  the  forts  are  provided  with  abund- 
ant bomb-proof  cover  for  the  garrison  and  supplies,  and 
with  chambers  in  which  the  guns  may  be  placed  when 
temporarily  silenced  by  the  concentrated  fire  of  the  attack. 

These  bomb-proofs  contain  the  wells,  kitchens,  bakeries, 
latrines,  hospitals,  telegraph  stations,  etc.  The  main  maga- 
zines are  placed  in  the  capital  traverse  or  under  the  flanks; 
service  magazines  near  the  guns,  and  niches  for  ammunition 
are  sometimes  made  in  the  interior  slope  of  the  parapet. 

The  masonry  arches  are  covered  with  earth  of  a thick- 
ness varying  from  3 to  16  feet,  depending  upon  the  fire  to 
which  they  are  exposed. 

Tor  important  points  which  must  be  held  at  all  hazards 
and  where  a great  command  and  wide  field  of  fire  is  wanted, 
revolving  turrets  are  proposed  and  are  strongly  advocated 
by  many  engineers,  foremost  among  whom  is  General 
Brialmont. 

When  the  gorges  of  the  forts  are  exposed  to  the  fire  of 
the  works  in  their  rear,  they  are  in  general  casemated 
masonry  structures,  which  serve  as  barracks  for  the  gar- 
rison, their  outer  walls  being  arranged  for  defence  against 
assault ; but  when  to  hold  a very  important  point  to  the  last 
extremity  the  works  are  thrown  so  far  to  the  front  as  to 
render  it  possible  that  they  may  be  surrounded,  the  gorges 
are  made  similar  to  the  faces,  but  may  have  less  cover  for 
their  scarp  walls  against  plunging  fire. 

Whenever  practicable  the  bomb-proofs  are  arranged  for 
defence  by  infantry  and  macliine  gun  fire,  and  serve  as  a 
substitute  for  the  older  form  of  keeps,  which  have  been 
generally  abandoned. 

168.  The  communication  with  the  exterior  is  through 
the  gorge  only,  by  a postern  provided  with  two  or  more 
barrier  doors  and  a drawbridge,  the  ditch  being  crossed  by 
a permanent  bridge  or  causeway,  which  is  protected  by  a 
casemated  guard-house. 


96 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


The  main  communication  in  the  interior  is  usually  a 
bomb-proof  gallery  from  the  gorge  to  the  salient,  under  the 
capita]  traverse,  which  also  covers  a row  of  chambers  on 
each  side  of  this  corridor.  This  central  communication  is 
sometimes  replaced  by  an  open  passage  similar  to  a chemin 
de  Tonde  at  the  level  of  the  parade  and  close  to  the  parade 
wall  or  rampart  slope,  giving  direct  access  to  the  chambers . 
under  the  terre-pleins  and  traverses. 

The  necessary  ramps,  stairs,  posterns,  and  lifts,  are  pro- 
vided in  either  case. 

169.  When  the  work  is  small,  and  its  importance  justi- 
fies the  expense,  the  whole  area  inside  the  interior  crest, 
except  the  gun  emplacements  and  the  banquettes,  may  be 
covered  by  chambers  and  passages  in  arched  masonry  and 
earth. 

170.  These  forts  are  surrounded  by  a glacis  covering  a 
sentmePs  path  extending  around  the  fort.  The  outworks 
are  restricted  to  flanking  caponnieres  and  redans  or  ravelins 
covering  the  caponnieres  and  bridge  at  the  gorge.  When 
wet  ditches  are  used  the  masonry  scarp  and  counterscarp 
walls  are  replaced  with  earthen  slopes. 

171.  If  there  is  difficulty  in  providing  places  for  the 
artillery  within  the  fort,  permanent  or  provisional  batteries 
for  4 to  6 guns  are  constructed  on  one  or  both  sides  of  the 
fort,  resting  their  flank  upon  the  gorge  or  shoulder  angle, 
and  having  their  interior  crest  at  the  height  of  the  glacis. 
They  are  supplied  with  ammunition  from  the  main  work. 

When  they  are  intended  to  be  worked  independently,  they 
are  provided  with  the  necessary  masks,  shelters,  magazines, 
etc. 

The  forts  are  placed  as  before  stated,  from  4 to  8 miles 
from  the  enceinte  and  2 to  3 miles  apart. 

172.  The  intermediate  works  are  calculated  for  a small 
infantry  garrison  of  from  60  to  100  men  and  3 or  4 pieces 
of  artillery,  usually  field  guns. 

They  are  generally  half  redoubts  or  lunettes  with  short 
flanks  and  straight  or  reentering  gorges.  They  have  a com- 
mand of  16  to  20  feet,  their  parapets  are  from  16  to  23  feet 
thick  on  the  faces  and  about  13  on  the  gorge.  Their  scarp 
walls  are  high  enough  to  resist  assault  (13  feet  minimum). 

The  arrangement  of  their  gorges  and  communications  is 
similar  to  that  of  the  larger  forts.  See  Plate  16,  Fig.  8. 


kjlements  of  permanent  fortification. 


CHAPTER  YU. 

I. 

INFLUENCE  OF  IRREGULARITIES  OF  SITE  ON  THE 
FORMS  AND  COMBINATIONS  OF  THE  ELEMENTS  OF 
PERMANENT  WORKS. 

173.  Although  the  same  general  principles  are  applica- 
ble, and  the  same  conditions  must  be  satisfied  in  planning 
a work,  so  that  it  shall  have  all  the  efficiency  of  which  it  is 
capable,  whether  the  site  is  unbroken  and  sensibly  hori- 
zontal, or  presents  a great  variety  of  feature,  within  the 
range  of  cannon  of  the  proposed  work  ; still  irregular  sites, 
where  the  surface  is  of  a diversified  character,  give  greater 
scope  than  level  ones  for  the  science  and  skill  of  the  en- 
gineer, and  call  for  all  the  resources  of  his  art  in  adapting 
his  plans  to  the  natural  features  of  the  site. 

The  principal  conditions  to  be  satisfied,  and  which  are 
the  same  in  all  cases,  are : 

1.  That  every  point  exterior  to  the  defences,  over  which 
the  enemy  must  approach  them,  or  from  which  he  can 
annoy  them  by  his  fire,  shall  be  brought  under  the  fire  of 
the  defences. 

2.  That  no  point  of  the  defences  shall  be  left  unguarded 
by  their  own  fire,  or  present  any  position  where  the  enemy, 
obtaining  temporary  shelter  from  fire,  may  gain  time  to  re- 
new an  onset. 

3.  That  the  troops  and  materiel  within  the  defences  shall 
be  sheltered  from  the  enemy’s  fire  in  any  position  he  may 
take  exterior  to  them. 

174.  The  problem  presented  for  solution  to  the  engineer 
in  irregular  sites  is  frequently  one  of  no  ordinary  complexity  ; 
demanding  a minute  and  laborious  study  of  the  natural 
features  of  the  position  in  their  relations  to  the  defence ; 
connected  with  a tentative  process  of  which  the  object  is  so 
to  modify  the  plan,  relief  and  details  ordinarily  adopted, 
as  to  adapt  them  in  the  best  manner  to  the  given  position. 


98 


ELEMENTS  OF  PERMANENT  FORTIFICATION - 


Ko  rules  but  of  a very  general  character  can  be  laid  down 
for  the  guidance  of  the  engineer  in  such  cases;  among 
which  the  following  are  the  most  essential,  and,  when,  prac- 
ticable, should  be  adhered  to. 

175.  It  has  already  been  observed  that,  from  the  means 
used  in  the  attack  by  regular  approaches,  the  more  plung- 
ing the  tire  of  the  work,  the  more  efficacious  will  it  prove 
in  retarding  the  enemy’s  progress.  The  efficiency  of  this 
tire  will  depend  upon  two  causes : 

1.  The  command  of  the  work  over  the  point  to  be  at- 
tained. 

2.  The  direction  of  the  ground  with  respect  to  the  lines 
by  wdiich  it  is  swept. 

176.  As  to  the  command  of  the  work  over  the  exterior 
ground,  it  has  already  been  shown  that  motives  of  economy 
restrict  it,  in  most  cases,  within  very  narrow  limits,  where, 
to  obtain  it,  artificial  embankments  have  to  be  employed. 

To  augment,  therefore,  in  the  greatest  degree  this  element 
of  the  defence,  advantage  should  be  taken  of  the  natural 
features  of  the  locality,  by  placing  the  principal  lines,  from 
which  the  exterior  ground  can  be  seen,  on  the  most  com- 
manding points  of  the  site. 

If,  with  this  position  given  to  the  principal  lines,  the 
ground  swept  falls  or  slopes  towards  them,  the  most  favor- 
able combination  for  an  efficacious  plunging  fire  wdll  be 
obtained ; for,  with  this  direction  of  the  ground,  the  enemy 
will  meet  with  far  greater  difficulty,  in  putting  himself  under 
shelter  by  his  works,  than  where  the  ground  falls  or  slopes 
from  the  line  by  which  it  is  swept ; as  the  surface,  in  the 
latter  case,  descending  in  the  rear  of  the  cover  thrown  up 
by  the  enemy,  will  be  screened  to  a greater  extent  tlian  in 
the  former,  where  it  rises  in  the  rear  of  the  cover. 

When  this,  however,  cannot  be  effected,  the  next  best 
-thing  to  be  done  is,  so  to  place  the  principal  lines  with 
respect  to  the  surface  to  be  swept  that  it  shall  be  seen  by 
a part  of  these  lines,  thus  bringing  to  bear  upon  it  a flank 
fire  from  these  parts. 

177.  The  general  rule,  therefore,  which  the  engineer  is 
to  take  as  a guide,  in  order  to  satisfy  the  condition  of  bring- 
ing the  exterior  ground  under  an  efficacious  fire  from  the 
work,  is : 

1.  To  place  the  principal  lines  of  his  worh  on  the  most 
commanding  points  of  the  site^  and  in  such  directions  as 
to  bring  the  exterior  ground  to  be  swept  in  a position  slop- 
ing towards  these  lines  in  such  a manner  that  they  can 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


1)9 


bring  their  entire  fire  to  hear  ^igyon  it^  or  else  bring  a por- 
tion of  it  to  sweep  it  in  f ront. 

This  will  generally  be  best  effected  by  placing  the  salient 
points  of  the  work  on  the  most  commanding  and  salient 
points  of  the  site ; as,  in  this  position  of  the  salients,  the 
faces,  which  are  usually  the  principal  lines  bearing  on  the 
exterior  ground,  will  occupy  the  salient  and  commanding 
portions  of  the  site,  whilst  the  reenterings,  being  thrown  on 
the  reentering  and  lower  portions  of  the  site,  will  be  in  the 
best  position  for  sweeping  the  ground  immediately  in  ad- 
vance of  the  faces  by  a flank  fii-e ; and  at  the  same  time 
these  reenterings  will  be  masked  by  the  faces  from  the 
enemy’s  view,  and  thus  preserved  from  serious  injury  up  to 
the  moment  when  their  action  may  be  rendered  most  effect- 
ive ; that  is  when  the  enemy,  despite  the  Are  from  the 
faces,  has  succeeded  in  planting  himself  upon  points  on 
which  this  Are  cannot  longer  be  brought  to  bear. 

To  carry  these  precepts,  which  are  equally  applicable  to 
.single  works  or  to  lines  of  detached  works,  into  practice,  a 
wide  margin  is  left  to  the  engineer’s  judgment,  in  which  he 
will  And  it  necessary  in  some  cases  to  extend  the  lines  of 
his  works  beyond  what  a strict  regard  to  economy  might 
prescribe,  so  as  to  include  within  his  defences  ground  from 
which  he  can  best  sweep  what  is  exterior  to  it,  or  which 
being  occupied  by  the  assailant,  might  make  his  own  posi- 
tion less  tenable,  in  this  way  forcing  him  to  extend  out  his 
lines  so  as  to  embrace  crests  within  them  that  overlook  val- 
leys beyond  them  ; and  in  some  cases  to  throw  his  own  lines 
further  back  in  order  to  avoid  enAlading  or  plunging  views 
from  points  which  are  too  distant  to  be  brought  within  his 
defences. 

2.  The  condition  of  tearing  no  point  of  the  defences 
unguarded  hy  the  fire^  will  depend  in  a great  degree  for  its 
fulAlment  on  the  same  rule  as  the  preceding.  But  where 
the  irregularity  of  the  site  is  such  that  all  the  exterior 
ground  cannot  be  swept  by  the  Are  of  the  works,  additional 
batteries,  advanced  works,  or  detached  forts  placed  in 
defensive  relations  with  the  main  works  must  be  employed. 

These  works  should  satisfy  the  usual  condition,  that  the 
more  advanced  must  be  taken  before  those  in  rear  can  be 
successfully  attacked. 

3.  The  condition  that  the  troops  and  materiel  within  the 
defences  shall  he  sheltered  from  the  enemf  s fire  from  all 
commanding  points  without.^  will  depend  upon  the  relative 
positions  of  the  principal  lines  and  the  exterior  commanding 


loo  ELEMENTS  OF  PERMANENT  FORTIFICATION. 

points;  and  as  far,  therefore,  as  it  can  be  done,  without 
sacrilicing  either  of  the  preceding  and  more  important  con- 
ditions, the  plan  of  the  work  should  be  so  arranged  that  the 
principal  lines  shall  present  themselves  in  the  most  favor- 
able direction  to  the  exterior  ground  to  avoid  plunging,  en- 
filading or  reverse  views  upon  their  terre-pleins  from  any 
point  of  it. 

178.  To  effect  these  objects,  when  the  work  is  in  the 
vicinity  of  commanding  heights  within  cannon  range,  and  the 
crests  of  these  heights,  as  seen  from  the  work,  present  a 
nearly  horizontal  outline,  the  principal  lines  of  the  work, 
fronting  the  heights,  should  receive  a direction  as  nearly 
parallel  as  practicable  to  that  of  the  commanding  crests. 

When  the  outline  of  the  crests  presents  a nearly  con- 
tinuous line,  but  one  which  declines  or  slopes  towards  the 
site  of  the  work,  the  principal  lines  towards  the  height 
should  receive  a direction  converging  towards  the  point 
where  the  line  of  the  crests,  as  seen,  if  prolonged,  would 
join  the  site,  if  this  point  or  points  beyond  it  and  within 
cannon  range  cannot  be  occupied  by  the  enemy. 

The  reasons  for  the  positions  assigned  to  the  principal 
lines  in  these  cases  respectively,  may  not,  at  a first  glance^ 
be  obvious ; but  by  examining  the  relative  positions  of  the 
crests  of  the  heights  and  of  the  principal  lines,  as  here  laid 
down,  it  will  without  difficulty  be  seen  that  they  can  be 
brought  in  the  same  plane,  and  the  latter  be  so  placed  as  to 
give  a nearly  uniform  command  to  the  parapets  of  the 
principal  lines  over  the  site ; and  that  by  keeping  the  terre- 
pleins  of  these  lines  in  planes  parallel  to  the  one  in  which 
the  crests  of  the  heights  and  those  of  the  parapets  are  held, 
and  at  suitable  levels  below  it,  the  parapets  will  be  made  to 
cover  the  terre-pleins  from  the  fire  of  the  heights  in  the 
simplest  manner. 

179.  Remarks.  The  foregoing  general  methods  for 
determining  the  direction  of  the  principal  lines  fronting 
commanding  heights,  so  as  to  cover  from  direct  fire,  in  the 
easiest  manner,  by  their  parapets,  the  space  to  the  rear  oc- 
cupied by  the  troops  and  materiel^  present,  at  the  same  time, 
the  simplest  cases  of  the  adaptation  of  the  plan  of  a work 
to  the  features  of  the  locality,  to  subserve  the  object  in 
view.  In  most  cases,  all  that  can  be  done  is  to  avoid  giving 
such  directions  to  any  of  the  principal  lines  as  shall  be  fa- 
vorable to  enfilading  or  reverse  views  of  the  enemy ; which 
may  be  effected  by  so  placing  them  that  their  prolongations 
shall  fall  on  points  where  the  enemy  cannot  establish  his- 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


101 


works ; or  on  those  which,  if  occupied  by  him,  will  afford 
disadvantageous  positions  for  his  batteries  either  for  enfilad- 
ing or  reverse  fires. 

As  the  attack  derives  its  great  advantage  from  its  envel- 
oping  position,  by  which  enfilading  views  and  a concen- 
trated fire  can  be  brought  to  bear  on  the  assailed  point,  so, 
in  the  general  disposition  of  his  defences,  the  engineer 
should  endeavor  to  reduce  these  salient  and  assailable  points 
to  the  fewest  number,  and  to  accumulate  upon  them  such 
surplus  strength  that  in  spite  of  their  natural  weakness  they 
will  cost  the  assailant  a great  deal  of  time  and  a large  sacri- 
fice of  means  to  get  possession. 

This  consideration  has  led  engineers  to  propose  for  the 
general  outline  of  their  defensive  polygon  a triangle  in 
which  the  principal  development  of  their  work  being  a num- 
ber of  fronts  on  a right  line,  they  can  neither  be  enveloped 
nor  their  principal  lines  be  enfiladed  by  the  assailant’s 
trenches,  thus  leaving  only  the  three  angular  points  as  assail- 
able, and  which  they  propose  to  strengthen  by  an  accumu- 
lation of  works  upon  them. 

Were  the  engineer  untrammelled  in  all  cases  by  other 
considerations,  this  method  might  do  very  well.  But  this 
is  far  from  being  the  case.  All  that  he  can,  therefore,  do  in 
planning  his  work  is  to  keep  this  consideration  in  view, 
throwing  as  many  fronts  as  he  can  on  the  same  right  line ; 
making  the  angles  of  his  general  polygon  as  open  as  possi- 
ble, so  as  to  force  the  assailant  to  a great  development  of  his 
works,  to  gain  a concentrated  and  enfilading  fire  on  them  ; 
placing  these  angles  on  points  of  difficult  access  to  the  as- 
sailant; and  by  taking  advantage  of  such  natural  obstacles 
as  water  and  rock,  to  give  additional  strength  to  these  points. 
The  skill  and  judgment  of  the  engineer  are  here  his  main 
reliance  in  adapting  his  details  to  these  general  principles. 


DEFILEMENt  OF  PERMANENT  WORKS. 

I 

180.  Remarks.  T|ie  greater  importance  of  so  adapting 
the  plan  and  command  pf  permanent  works  to  the  features 
of  irregular  sites  as  tolsatisfy  the  conditions  of  sweeping 
thoroughly  by  their  fiif  all  aj^proaches  exterior  to  the  de- 
fences, and  completely  tanking  the  latter,  seldom  places  it 
in  the  power  of  the  engineer  to  fulfil  the  condition  of  with- 


102  ELEMENTS  OF  PERMANENT  FORTIFICATION. 

I 

drawing  the  interior  of  the  defences  from  either  enfilading 
or  reverse  views  by  a modification  of  either  the  plan  or  the 
command.  f 

To  mask,  therefore,  the  terre-plein  which  would  be  ex- 
posed to  these  fires,  as  well  as  from  such  as  would  be  at- 
tained by  a plunging  fire  in  front,  resort  must  be  had  to  the 
usual  expedients  of  defilement ; that  is,  giving  to  the  terre- 
plein  s such  position  with  respect  to  their  parapets  that  the 
troops  and  materiel  upon  them  will  be  screened  from  a 
plunging  fire  in  front  by  the  parapets ; and,  when  the  terre> 
pleins  are  exposed  to  either  enfilading  or  reverse  views,  by 
so  placing  earthen  traverses  or  other  masks  as  to  intercept 
these  views,  and  cover  the  troops,  etc.,  from  the  enemy’s 
projectiles. 

The  defilement  of  permanent  works,  like  that  of  field 
works,  proposes  the  same  end,  and  employs  nearly  the  same 
means.  They  differ  mainly  in  their  practical  details ; the 
latter  being  reduced  to  a simple  practical  operation  on  the 
field,  while  the  former,  from  the  usually  greater  complex- 
ity of  the  arrangements  of  permanent  defences,  requires  the 
aid  of  mathematical  methods,  and  demands  the  best  attain- 
able results. 

Owing  to  the  regularity  of  the  trajectory  of  modern  rifles 
and  the  resulting  accuracy  of  fire  even  with  an  angle  of  fall 
up  to  \ or  greater,  it  is  generally  impracticable  to  secure 
cover  from  cannon  fire  for  any  considerable  area  by  the  de- 
filement of  open  defences.  However,  as  the  assailant  must 
in  general  see  the  effect  of  his  fire,  both  to  correct  his  aim, 
and  to  learn  whether  his  results  justify  the  expenditure  of 
ammunition,  the  necessity  for  defilement  from  the  view  of 
the  attacking  force,  when  it  can  be  had  at  not  too  great  cosri 
still  exists. 

The  protection  of  the  larger  areas  from  plunging,  reverse 
and  enfilade  fire  must  ^be  secured  by  bomb-proofs ; for 
limited  areas  it  may  be-  obtained  by  the  free  use  of  the 
traverse  and  parados. 

181.  For  the  solution  of  all  problems  of  the  defilement 
of  permanent  works,  the  engineer  requires — 

1.  The  limit  exterior  to  the  defences  beyond  which  the 
effect  of  the  enemy’s  fire  may  be  regarded  as  so  uncertain 
as  to  be  neglected,  and  that  beyond  which  he  will  be  una- 
ble to  see  the  point  struck  and  the  effect  produced  by  his 
projectiles. 

2.  The  presumed  positions  within  this  limit  that  the  en- 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


103 


emy  may  take  up  to  bring  his  artillery  to  bear  upon  the 
works,  or  for  observatories. 

3.  An  accurate  topographical  map  of  all  the  ground  within 
the  above  limits,  as  given  by  its  horizontal  curves  referred 
to  a plane  of  comparison. 

4.  The  magistrals  and  interior  crests  of  the  works,  as 
either  definitely  or  proximately  arranged,  referred  to  the 
same  plane. 

182.  The  15c.  m.  (6")  rifle,  the  largest  considered  available 
for  siege  purposes,  is  effective  for  accurate  breaching  fire  for 
masonry  up  to  2000  yards,  angle ^of  fall  about  3°  ; for  flank 
fire  against  gun  emplacements  up  to  3500  yards  (angle  of  tall 
6j°).  Its  extreme  range  is  about  10,500  yards,  or  6 miles. 

The  distance  at  which  the  point  of  striking  and  effect  of 
the  shot  can  be  determined  by  the  use  of  field  glasses  and 
portable  telescopes  is  from  1 to  2 miles. 

183.  These  limits,  and  the  importance  of  protecting  any 
particular  points  within  the  work,  will  determine  the  charac- 
ter of  defilade  to  be  adopted. 

The  surface  of  the  site  embraced  within  the  exterior  lim- 
its and  the  line  of  defences  may  be  divided  into  three  zones, 
one  lyiug  between  the  Iffnits  and  position  of  the  first  paral- 
lel of  the  attack ; the  second  between  the  positions  of  the 
first  and  second  parallels ; the  third  between  the  positions 
of  the  second  and  third  parallels. 

184.  At  no  stage  |bf  the  attack  will  the  assailant  at- 
tempt to  raise  his  batteries  above  the  natural  surface  of  the 
ground,  in  order  to  olitain  command  for  his  guns  ; the  labor 
and  additional  exposure  of  his  guns  to  the  fire  of  the  de- 
fence far  more  than  Counterbalancing  the  advantage  gained 
by  any  attainable  increase  in  command.  This  will  restrict 
the  vertical  limit  wifhin  which  his  fire  may  be  delivered  to 
about  5 feet  above  t^e  surface  of  the  ground. 

185.  Observatories  or  lookouts  will  be  placed  at  the 
highest  points  whicfi  can  be  occupied  with  moderate  secur- 
ity ; but  no  great  height  can  be  given  them  above  the  gen- 
eral line  of  the  wojtks  without  an  amount  of  work  incom- 
mensurate with  tile  small  advantage  gained  in  the  first 
2one  or  exposing  tl:®m  to  the  destructive  fire  of  the  defence 
in  the  second  and  tjiird. 

These  considerations  will,  in  general,  limit  the  height  of 
the  observatories  to  10  feet  above  the  ground  in  the  first 
ind  second  zones.  < In  the  third  zone,  the  defilade  will  be 
igainst  close  fire  abd  a nearly  straight  trajectory.  In  this 
cone  the  fire  of  infantry  mounted  on  the  parapets  of  the 


104 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


trenches  may  sometimes  be  used,  and  the  work  should  be 
defiled  against  it.  The  maximum  height  of  this  plane  of 
fire  may  also  be  taken  at  ten  feet  above  the  level  of  the  site. 

186.  Taking,  then,  the  extreme  cannon  range  or  the 
adopted  limit  of  distinct  sight,  the  dangerous  ground  exte- 
rior to  line  of  the  defences  may  be  marked  out  on  the  top- 
ographical map  of  the  site  by  drawing  lines  parallel  to 
th^ose  connecting  the  most  advanced  salients  and  at  this 
distance  from  them  and  then  considering  the  references  of 
the  horizontal  curves  of  the  ground  within  the  zones  thus 
marked  otf  to  be  increased  10  feet. 

187.  In  the  defilement  of  each  part  separately  of  the  line 
of  defences,  those  portions  alone  of  these  zones  should  be 
regarded  as  dangerous  which  are  embraced  within  arcs,  or 
other  lines  drawn  at  the  foregoing  distances  from  the  sal- 
ients, or  the  faces  of  the  part  to  be  defiled. 

It  may  also  happen  that,  within  the  limits  of  dangerous 
ground  for  one  portion  of  the  line  of  defences,  there  may 
be  other  portions  which,  from  their  positions,  may  mask 
the  portion  to  be  defiled  from  all  the  dangerous  points  be- 
yond them ; in  which  case  the  points  thus  shut  off  need  not 
be  regarded,  in  effecting  the  operations  of  defilement. 

If,  for  example  * (PI.  17,  Fig  1),  the  limits  of  dangerous 
ground  for  the  demi-lune  a being  marked  off,  it  is  found 
that  the  demi-lune  b,  masks  the  demi  lune  a from  all  fire 
that  might  come  from  the  ground  beyond  b ; then  this 
portion  of  the  zones  of  danger  need  not  be  regarded  in  de- 
filing A. 

To  ascertain  this  it  will  only  be  necessary  to  pass  a plane 
through  the  interior  crest  of  a tangent  to  the  surface  beyond 
B,  raised  10  feet,  and  see  whether  it  lies  below  b at  all 
points.  If  so  then  will  b serve  as  a mask  for  a. 

188.  All  masonry  should  be  covered  by  earthen  masks 
from  the  plunging  fire  of  the  heaviest  guns  within  the 
range  at  which  this  fire  would  prove  destructive  against  it. 

189.  In  the  defilement  of  works  of  limited  interior  capac- 
ity, as,  for  example,  the  reduit  of  the  reentering  place-of- 
arms,  the  double  caponniere  and  the  like,  which  are,  more- 
over, not  habitually  occupied  by  troops,  the  extreme  limits 
may  be  reduced. 

190.  Within  the  limits  of  the  zones  of  danger,  positions 
may  be  found  for  front,  for  reverse,  and  for  enfilading  fire. 

If  the  two  faces,  for  example,  of  a work  be  prolonged  to 
intersect  the  extreme  limit  of  dangerous  ground,  the  sector 
which  they  embrace  may  be  termed  the  limit  of  direct  or 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


105 


J^Tontfire  * since,  from  every  position  that  can  be  taken  np 
within  this  sector,  a direct  fire  alone  can  be  brought  to  bear 
upon  the  two  faces. 

The  two  sectors  wliich  lie  adjacent  to  this  may  be  termed 
the  limits  of  lateral^  or  reverse  fire^  since  they  afford  posi- 
tions from  which  a reverse  fire  can  be  obtained  against  one 
of  the  faces,  and  a front  fire  upon  the  other.  It  is  also  only 
within  these  last  limits  that  positions  for  enfilading  the 
terre-pleins  of  the  faces  can  be  obtained. 

191.  Remarks.  The  problems  of  defilement  which  pre- 
sent themselves  for  solution  may  embrace  one  or  more  of 
these  cases  in  any  example ; depending  upon  the  relative 
positions  of  the  interior  crest  of  the  work  to  be  defiled,  and 
of  the  dangerous  ground  embraced  within  the  foregoing 
limits. 

The  terre-pleins  may  be  screened  from  direct  view  by 
their  parapets,  from  reverse  or  enfilade  view  on  one  face 
alone,  in  some  cases  by  the  parapet  of  the  other,  in  others 
by  traverses  and  parados. 

A portion  of  the  terre-pleins  may  be  screened  from  plung- 
ing fire  by  the  parapet,  parados  or  traverses,  but  for  pro- 
tecting considerable  areas,  bomb-proof  casemates  or  shelters 
are  required,  as  previously  stated. 

III. 

PROBLEMS  OF  DEFILEMENT. 

192.  It  does  not  come  within  the  scope  of  this  sum- 
mary to  examine  the  many  cases  of  defilement  which  may 
arise  from  irregularities  in  the  site.  Those  alone  will  be 
discussed  which  are  of  most  ordinary  occurrence,  and  which 
require  for  their  solution  the  usual  geometrical  constructions 
involved  in  planes  and  other  surfaces  tangent  and  secant  to 
a surface  defined  by  the  projection  of  its  horizontal  curves. 
The  cases  which  will  here  find  their  application  may  be 
arranged  under  two  heads : 

1.  The  plan  and  command  of  a work  being  definitely  de- 
cided upon,  to  ascertain  the  exact  portions  of  the  zones  of 
danger,  from  which  any  description  of  fire  can  be  brought 
to  bear  upon  its  terre-pleins,  and  to  defile  them  from  it, 

2.  The  plan  of  a work  being  definitely  fixed,  but  its  com- 
mand only  approximately  within  certain  limits,  to  ascertain 
.the  easiest  method  of  defiling  the  terre-pleins  of  the  work. 


106  ELEMEJifTS  OF  PEK]^Z^ENT  FORTIFICATION. 

/ 

b;^  varying  the  command/or  position  of  the  interior  cresty 
within  the  assigned  limitSL 

193.  (Prob.  1,  PI.  17|'  Fig.  2.)  The  command  or  posi- 
tion of  the  interior  cresf  of  the  faces  of  a worh  being  fixed, 
to  ascertain  the  dangerous  points  on  the  exterior y and  to 
defile  its  terre-plein  from  these  points. 

Let  a b,  a c,  be  the  projections  of  the  given  crest ; and 
the  curves  (26.0),  (2Q.0),  etc.,ythose  of  the  natural  surface. 

Prolong  outwards  to  c and  d,  the  faces ; construct  the  scales 
of  declivity  of  the  two  lines,  a e,  a d ; and,  from  them,  the 
scale  of  declivity,  e f,  of  their  plane. 

From  the  salient,  a,  supposing  an  arc  to  be  described 
with  a radius  of  3h00  yards,  the  dangerous  ground  will  be 
included  between  and  the  two  faces  of  the  work. 

Now,  if  the  plane  of  the  interior  crests,  of  which  e f is 
the  scale  of  declivity,  be  indefinitely  extended,  and  its  inter- 
section with  the  Surface  parallel  to  the  natural  surface  and 
10  feet  above  it  be  found,  it  is  evident  that  the  portion  of 
this  raised  surfacie  which  lies  below  the  plane  may  be  dis- 
regarded, as  the  interior  of  the  work  is  covered  from  it  by 
the  parapet.  But  from  every  point  of  the  surface  above 
the  plane  the  inferior  is  more  or  less  exposed  to  view,  de- 
pending upon  the  height  of  the  point  above  the  plane,  its 
distance  from  thq  work,  and  the  height  of  the  interior  crest, 
above  the  terre-plein  and  parade. 

Having  drawn  the  horizontals  of  the  plane,  e f,  and  found 
their  intersections:  with  the  corresponding  horizontals  of  the 
raised  surface  (which  last  will  be  given  by  adding  10  feet  to 
the  references  of  the  curves  of  the  ground),  of  which  x y z 
is  the  projection, : that  portion  of  the  surface  which  lies 
abo'^e  this  curve  wdl  alone  see  the  interior  of  the  work,  and 
will  be  the  only  portion  for  which  defilement  will  be  neces- 
sary. ‘ 

Now,  as  this  intersection  falls  entirely  within  the  angle 
d a e,  of  the  faces  prolonged,  or  within  the  limits  of  front 
fire,  it  is  evident  that  the  terre-pleins  wdll  require  to  be  de- 
filed only  from  direct  fire. 

To  efiect  this,  let  a plane  be  passed  through  the  face, 
b a d,  of  the  work,  atid  tangent  to  the  raised  surface  above 
X y z.  This  plane  will  pass  above  all  the  dangerous  ground, 
except  at  its  point  oB  contact  with  it ; and,  being  extended 
back  from  the  face  wifhin  the  work,  it  is  clear,  if  the  terre- 
plein  of  this  face  be  soHaken  with  respect  to  this  plane  that 
no  point  of  it  shall  be  less  than  8 feet  below  the  plane,  that 
then  every  point  of  the  terre-plein  will  be  screened  from 


ELEMENTS  OF  PERMANENT/FORTIFICATION. 


107 


view  by  tbe  parapet  of  the  fa^  a b.  I^ow,  if  the  same 
series  of  operations  be  gone  /hrough  with  for  the  face, 
c a e,  then  will  its  terre-plein  defiled  in  like  manner ; and 
thus  the  defilement  of  the  jivhole  work  be  completed  for 
this  case.  / 

The  tangent  planes  whicM  satisfy  the  above  conditions  are 
termed  Planes  of  Direct  pefilement  j and  they  may  be  de- 
fined as  the  planes  whichJ passed  through  the  interior  crest 
of  a parapet^  leave  at  jleast  10  feet  helow  them^  all  the 
dangerous  ground  of  front  fre,  and  pass  at  least  8 feet 
above  every  point  of  thi  terre-plein  behind  the  parapet. 

The  terre-pleins  ar^  usually  parallel  to  their  respective 
planes  of  direct  defilement  and  8 feet  below  them.  But 
when  the  declivity  of  the  plane  of  defilement  exceeds 
then  the  terre-plein,  Jf  it  is  to  receive  cannon  mounted  on 
travelling  carriages,  ^ust  be  kept  within  this  limit. 

In  Fig.  2,  the  re:^rences  are  given  in  feet  The  tangent 
plane  through  b a is  determined  in  the  usual  manner,  by 
finding  the  horizontal  (in  this  case  45.0),  among  all  those 
drawn  to  the  cur^bs  of  the  raised  surface,  which  makes  the 
minimum  angle  w|th  b d.  The  line  h i,  perpendicular  to  this 
horizontal,  is  the|scale  of  declivity  of  this  plane ; and  the 
point,  p,  that  of  -Contact.  The  line  k 1,  is,  in  like  manner, 
the  scale  of  declivity  of  the  other  plane,  and  o its  point  of 
contact.  i 

It  might  happen,  from  the  steepness  of  the  terre-pleins, 
that  the  reenteHng  or  gutter  formed  at  their  intersection 
would  be  inconvenient,  and  it  would  therefore  be  desirable 
to  have  this  position  raised,  when  it  can  be  done  without 
exposure  to  a plunging  fire. 

This,  in  most  cases,  may  be  effected  in  this  way : It  will 
be  seen,  from  an  inspection  of  Fig.  2,  that  the  points  o and 
p are  the  only  ones  from  which  the  enemy’s  fire  passes  ex- 
actly at  8 feet  above  all  the  points  of  the  respective  terre- 
pleins  determined  by  the  tangent  planes ; and  that  if,  from 
these  points,  lines  of  fire,  oar  and  p a s,  be  drawn,  every 
other  line  of  fire  through  a,  from  the  ground  in  the  angle, 
p a o,  will  pass  more  than  8 feet  above  the  portion  of  the 
terre-pleins  embraced  in  the  angle,  s a r,  since  the  ground 
within  the  exterior  angle  lies  below  the  tangent  planes. 

If,  then,  a be  taken  as  the  vertex  of  a cone,  the  elements 
of  which  are  tangent  to  the  raised  surface'  within  the  angle, 
p a o,  and  if  these  elements  be  prolonged  within  the  work, 
their  prolongation  will  form  a cone  of  lines  of  fire,  which 
will  pass  more  than  8 feet  above  the  terre-pleins.  If  these 


i 


108 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


last,  therefore,  be  connected  by  surface  parallel  to  this 
cone,  and  8 feet  below  it,  this  surface  may  be  taken  as  the 
portion  of  the  terre-plein  which,  Connecting  the  two  plane 
portions,  will  remedy  the  inconvenience  pointed  out. 

194.  (Prob.  2,  Fig.  3.)  Theldcota  being  the  same  as  in 
the  preceding  case,  and  the  vprh  being  exposed  to  both 
direct  and  reverse  views,  to  cover  its  interior  from  these 
views.  I 

Suppose  the  plane  of  the  inferior  crest  of  the  faces  ex- 
tended within  the  limits,  ann  its  intersection  with  the 
dangerous  ground  determined  as  in  the  preceding  case  ; and 
let  X y z,  m n o,  and  p q r,  be  the  curves  of  this  intersection. 
The  face  a b will  be  exposid  to  direct  fire  alone  from  the 
above  the  two  curvesl  x y z and  m n o ; and  to  re- 
verse fire  from  that  above  thq  curve  p q r.  In  like  manner, 

to  direct  fire  from  x y z and 
i m n o. 

e from  the  direct  fire  will  be 
way  as  in  the  preceding  Prob. 


the  scales  of  declivity  of  the 
the  faces  respectively, 
a plane  is  passed  through  a b, 
p q r ; and 


one  through  a c. 


ground 

V 

the  face  a c will  be  exposed 
p q r,  and  to  reverse  fire  froi 
The  defilement  of  each  faj 
effected  precisely  in  the  sam< 

The  lines  h i and  k 1 arc 
planes  of  direct  defilement  oj 
For  the  reverse  defilemeni 
tangent  to  the  surface  abo^ 
tangent  to  the  surface  abovejm  n o,  and  their  line  of  inter- 
section a a'  found.  The  line|u  v is  the  scale  of  declivity  of 
one  of  these  planes,  termed  ai  Plane  of  Reverse  Defilement, 
and  s t that  of  the  other.  | 

Now,  if  a traverse  is  so  plaped  that  its  crest  shall  occupy 
the  position  of  the  line  a a',  i|  will  cover  all  between  it  and 
the  two  faces,  as  high  as  the  itterior  crests,  from  the  reverse 
fire  on  each  side.  But  as  it  i^  desirable  to  have  the  troops, 
when  on  the  banquettes,  screened  from  this  fire,  the  crest  of 
the  traverse  should  be  raised  from  18  inches  to  2 feet  above 
the  line  a a'  to  effect  this. 

The  traverse  should  extend  so  far  towards  the  gorge  of 
the  work  that  the  entire  line  of  each  face  shall  be  covered 
by  it.  To  determine  its  length  with  this  condition,  lines 
are  drawn  from  the  extreme  points  b and  c of  the  faces, 
tangent  to  the  curves  m n o and  p q r,  and  their  points  of 
intersection  with  a a'  marked  ; the  one  that  falls  farthest 
from  the  salient  will  evidently  give  the  required  length. 

If  the  line  a a'  should  fall  so  near  either  of  the  faces  that 
the  traverse,  if  placed  along  it,  would  incommode  the  ser- 
vice of  that  part  of  the  w^ork,  it  will  be  the  best  to  place  its 
crest  in  the  vertical  plane  a a"  of  the  capital  of  the  work. 


ELEMENTS  OF  PERMANENT  BORTIFICATION. 


109 


Wlien  so  placed,  the  intersection  m this  vertical  plane  with 
each  of  the  planes  of  reverse  demeinent  must  be  found,  and 
the  crest  of  the  traverse  be  tah4n  18  inches  above  the  one 
that  lies  highest. 

195.  The  position  of  the/crest  of  the  traverse,  as  deter- 
mined by  either  of  the  preceding  methods,  will  be  in  a 
vertical  plane  passing  throi^h  the  salient,  a,  of  the  work. 

From  the  thickness  and  slopes  which  traverses  usually 
receive,  they  would  ordinarily,  if  placed  in  this  position, 
take  up  all  the  interior  aq^ace  within  the  salient,  and  leave 
no  room  there  for  dispositions  either  for  artillery  or  mus- 
ketry. To  prevent  thife,  a break  is  made  in  the  direction 
of  the  crest,  at  some  homt  on  the  vertical  plane  through 
the  salient,  from  whicj  it  is  directed  on  a point  of  either  of 
the  faces,  so  far  from  the  salient  that  sufficient  room  will 
be  left  for  the  objectnn  view.  In  (Fig.  4),  which  illustrates 
this  arrangement,  tMe  traverse  is  withdrawn  far  enough 
from  the  salient  tof leave  room  for  a barbette  battery  for 
several  guns.  I 

The  face  upon  which  the  traverse  is  directed,  will  be  de- 
termined by  the  condition  of  covering  both  faces  in  the  most 
effective  manner,  l|y  the  position  taken  for  the  traverse. 

196.  The  crossfsection  of  traverses  for  permanent  w^orks 
is  similar  to  those msed  in  field  works.  The  top  of  the  trav- 
erse receives  a sl^ht  slope  each  w-ay  from  the  crest  to  the 
sides.  The  thiclAess  at  top  is  sufficient  to  render  it  shot- 
proof.  The  side!  take  the  natural  slope  from  the  top,  either 
to  the  lowest  lev|l  at  which  they  may  be  struck  or  to  the 
terre-plein.  If  |to  gain  interior  space  these  slopes  are 
terminated  at  thmiigher  level,  then  the  portions  of  the  trav- 
erse below  these  blanes  are  made  more  steep,  and  the  earth 
supported  by  retaining  walls.  The  top  of  the  traverse, 
wdiere  it  joins  tl|e  parapet,  being  higher  than  the  superior 
slope,  is  run  oiA  above  this  slope,  upon  which  the  side 
slopes  fall ; its  e|s:tremity  terminates  in  the  plane  of  the  ex- 
terior slope,  ext^ded  above  the  exterior  crest. 

197.  When,  tfrom  any  circumstance,  a single  traverse 
cannot  be  used  Ifor  reverse  defilement,  resort  must  be  had 
to  several,  which  should  be  so  combined  that  no  line  of  fire 
can  penetrate  between  their  extremities  to  attain  any  point 
which  they  shofild  cover. 

Examples  of  Ms  construction  are  found  in  several  plates, 
and  will  suggest  the  manner  of  making  others.  The  fol- 
lowing case  will  serve  as  a further  illustration : 

Where  a demi-lune  is  arranged  wdth  a reduit,  a traverse 


110  ELEMENTS  OF  PERMANENT  FOI^IFICATION. 

placed  in  its  salient  cannot  be  extended  further  back  than 
the  counterscarp  of  the  reduit ; .and/an  open  space,  there- 
fore, will  be  left  at  the  ditch,  throu^  which  a reverse  fire 
would  attain  that  portion  of  either  face  which  is  not  covered 
either  by  the  traverse  in  the  saliemt,  or  by  the  parapet  of 
the  reduit.  / 

To  cover  the  part  thus  expose<l,  it  will  be  necessary  to 
place  one  or  more  traverses,  wh/ch,  in  combination  with 
the  one  in  the  salient,  and  the  pyapet  of  the  redoubt,  shall 
subserve  this  end.  I 

To  simplify  the  case,  let  the  face  a c,  PI.  17,  Fig.  5,  be 
the  one  exposed,  and  let  the  point  x be  one  the  tire  of 
which  is  most  dangerous.  H^ing,  in  the  first  place  ar- 
ranged the  traverse,  t,  as  in  me  last  example,  and  drawn 
the  two  lines  of  fire  x b and  x|d  from  the  point  x,  through 
the  extremity  of  the  traverse,  fnd  the  top  of  the  parapet  of 
the  redoubt  at  the  salient,  the  length,  b d,  of  the  face  inter- 
cepted between  these  I'nes  will  be  the  part  to  be  covered. 
If  a second  traverse,  t',  be  pfcced  across  the  terre-plein  of 
the  other  face  of  the  demi-lune,  and  in  a position  such  that 
one  of  its  ends  shall  rest  on|  x b,  and  the  other  on  x d,  it 
will  evidently  cover  the  port^n  b d. 

198.  In  selecting  the  posifions  of  several  combined  trav- 
erses, attention  must  be  given  to  avoid  those  where,  if  one 
be  placed,  the  assailant  would  find  shelter  behind  it  from 
the  fire  from  the  rear.  In  tl|e  example  just  taken,  the  slope 
of  t,  towards  the  salient,  should  be  swept  by  the  fire  from 
the  rear,  through  the  reduit  ditch  ; the  like  slope  of  t' 
should  be  swept  by  a portion  of  the  reduit  face  near  its 
salient ; and  neither  so  fall  as  to  have  the  space  behind  it 
masked  from  fire  by  the  one  to  its  rear. 

199.  Remarks.  Traverses  usually  present  not  only  the 
easiest  solution  of  all  problems  of  reverse  and  enfilading 
defilement,  but,  affording  the  means  of  rendering  the  com- 
mand independent  of  fere  from  without,  they  enable  the 
engineer  to  regulate  this  element  solely  with  a view  to  the 
effect  which  he  desires  to  attain  by  his  own  fire. 

From  the  space  required  for  their  erection,  traverses  may, 
as  in  the  cases  of  narrow  terre-pleins,  like  those  of  the 
covered-ways,  and  of  the  demi-lune  with  a redoubt,  be  in- 
convenient, both  from  embarrassing  the  communications, 
and  from  taking  up  ground  that  may  be  wanted  for  bat- 
teries. 

200.  (Prob.  3.)  The  plan  of  a bastion  heing  dejmitively 
Jixed^  and  one  point  of  its  command  apgiroximately^  to  de- 


ELEMENTS  OF  PERMANENT  FORTIFICATION.  Ill 

Jile  the  work  in  the  most  advantageous  manner^  hy  shifting 
the  position  of  its  interior  f rest  within  certain  limits. 

Let  Fi^.  6 be  the  plan  Vi  the  work,  and  a the  salient,  the 
command  of  which  canbh  varied  within  certain  limits  with- 
out impairing  anj  of  th,^  other  conditions  ; and  let  the  dan- 
gerous ground  be  enabraced  within  the  arc  m n,  at  3500 
yards  from  a,  and  tj^e  lines  a u and  a v supposed  drawn 
from  a,  through  coy^Ving  masses  on  the  right  and  left  of  the 
work.  / 

The  front  limit^ of  defilement  in  this  case  are  embraced 
within  the  sector  In  a n ; and  the  lateral  limits  within  the 
other  two  m a uAnd  n a v.  Now,  the  most  favorable  case 
of  defilement  h^e  will  be  that  where  a plane,  containing  a, 
taken  within  it#  extreme  positions,  shall  pass  above  all  the 
exterior  grounip,  and  give  such  a command  to  the  interior 
crest  throughout,  when  held  in  it,  as  shall  satisfy  the  otlier 
conditions  of/idefence.  To  ascertain  the  existence  of  such  a 
plane,  let  a 1^  taken  as  the  vertex  of  a cone  which  envelops 
all  the  dan^rous  ground ; any  plane  tangent  to  this  cone 
will  satisfy  ahe  condition  of  defilement,  and  it  will,  there- 
fore, only  Jbe  necessary  to  find  whether  any  one  of  these 
planes  of  ^defilement  will  satisfy  the  other,  of  giving  the 
points  b CiM,  and  e,  a suitable  command.  If  no  such  plane 
can  be  obtained,  the  next  most  favorable  case  will  be  to  find 
one  thatlshall  satisfy  all  the  requisite  conditions  of  com- 
mand, arid  intersect  the  ground  only  within  the  front  limits. 
In  this  ^se  it  is  clear,  from  the  position  of  this  plane,  if  the 
interiorfcrests  are  held  in  it,  that  the  interior  of  the  work 
will  be  Exposed  only  to  the  direct  fire  from  that  portion  of 
the  grojind  which  lies  above  the  plane. 

Let  i y z be  the  curve  of  intersection  of  the  plane  with 
the  ground,  found  in  the  usual  way.  Through  the  faces  a b 
and  a let  planes  of  direct  defilement  be  passed  ; the  terre- 
plein  bf  the  faces  being  held  parallel  to  them  will  be  covered 
by  thkir  respective  parapets  from  all  plunging  fii’e.  But, 
in  or^er  that  the  planes  of  defilement  of  the  faces  shall  also 
defil^  the  flanks,  it  is  necessary  that  each  flank  be  'olaced  in 
the  -plane  of  defilement  of  the  adjacent  face,  and  its  terre- 
plein  in  that  of  the  terre-plein  of  the  face.  Now,  in  giving 
the  interior  crests  of  the  flanks  these  new  positions,  they 
will  lie  below  the  plane  that  contains  the  curve,  x y z,  and 
in  which  the  interior  crests  of  the  faces  lie.  This  being  the 
case,  it  may  happen  that  the  parapet  of  one  of  the  flanks 
will  not  cover  the  opposite  face  from  reverse  fire,  coming 
from  the  lateral  limits  opposite  the  flank.  In  this  con- 


lU 


ELEMENTS  OF  PERMANENT  FOMIFICATION. 


tiiigency,  it  will  be  necessary,  in  ord^  to  cover  the  face,  to 
place  the  flank  in  the  plane  of  the  ciy  ve,  x y z,  as  this  plane 
detiles  from  the  lateral  limits  ; but,/n  doing  this,  the  flank, 
d e,  for  example,  will  be  exposed,  Jh  its  turn,  to  the  ground 
above  x y z ; and  to  cover  it,  the  pnly  remedy  is  to  erect  a 
traverse,  at  some  suitable  point,/which  shall  intercept  all 
this  dangerous  fire.  The  least  iiponvenient  position  for  the , 
traverse  will  usually  be  at  the  Aoulder  angle.  From  this 
point  it  must  extend  so  far  bacM  as  to  intercept  all  fire  from 
above  x y z,  both  on  the  terr^pleins  of  the  flank  and  cur- 
tain, where  they  unite,  and  b^  high  enough  to  screen  the 
troops  on  the  banquette.  | 

If  the  defilement  cannot  pe  effected  by  either  of  these 
processes,  there  remains  no  pther  means  than,  having  first 
definitely  fixed  the  comim^d,  to  divide  the  bastion  by  a 
traverse,  either  along  its  capital,  or  some  other  convenient 
direction,  and,  having  giv^  it  a suitable  height,  to  cover 
each  portion  from  direct  fi|e  by  the  usual  method. 

201.  The  foregoing  pr<|blems  embrace  in  their  solution 
all  of  the  more  ordinary  ci^es  of  defilement,  and  suggest  the 
route  to  be  followed  in  tr^ting  others. 

In  all  cases  of  the  defile|nent  of  combined  works,  like  the 
enceinte  and  its  outworks,  etc.,  it  must  be  borne  in  mind 
that  the  advanced  wmrks,; which  from  their  position,  must 
first  fall  into  the  assailant^  power,  become  thus  a portion  of 
the  dangerous  ground  for  the  works  more  retired,  and 
which  must  also  be  held  after  the  fall  of  the  others.  The 
retired  works,  under  such  circumstances,  must  be  defiled 
from  the  advanced  ; their  planes  of  defilement  being  made 
to  pass  from  3 feet  to  4.5  feet  above  the  portion  of  the  ad- 
vanced work  on  which  it  is  presumed  the  assailant  may 
make  a lodgment,  and,  which,  from  its  position,  may  be  re- 
regarded as  the  most  dangerous  to  the  retired  work,  it  being 
assumed  that  in  the  close  attack  the  artillery  fire  will  be  de- 
livered at  a height  above  the  ground  not  greater  than  this. 

202.  Where  a work  has  considerable  command,  and  is 
open  at  the  gorge  like  the  cavalier  retrenchments,  for  vx- 
ample,  and  the  works  in  its  rear  do  not  mask  its  interior 
from  reverse  fire,  it  may  be  necessary  to  place  a traverse, 
termed  2^ parados^  across  its  terre-plein  at  the  gorge,  giving 
it  sufficient  height  to  subserve  the  end  in  view. 

A parados  or  traverse  immediately  in  rear  of  a parapet 
exposed  to  front  fire  is  open  to  objection,  since  shells 
passing  over  the  parapet  penetrate  the  traverse  and  by  their 


ELEMENTS  OF  PERMANENT  FORTHTCATION. 


113 


Itageoiis. 


ected  to  fire  of  greater  calibres^ 


explosion  throw  out  splinters  and  porfions  of  the  traverse 
toward  the  parapet.  / 

On  the  other  hand,  they  intercep^/splinters  coming  from 
shells  exploding  in  their  rear,  and  .'^hen  properly  construc- 
ted, of  soft  earth,  retain  a very  lai*ge  portion  of  the  splinters 
of  shells  exploding  after  striking^them. 

The  following  conclusions  we/e  drawn  from  the  results 
of  an  exhaustive  series  of  exp^dments  recently  carried  on 
in  Italy  Fortifications  of  T^-day,”  Washington,  Govern- 
ment Printing  Oifice,  1883) ; 

‘‘1.  In  temporary  batteri^,  and  also  in  permanent  ones 
which  can  only  be  attacked  Joy  field  or  siege  artillery,  para- 
dos, even  at  short  distances/are  not  only  free  from  danger, 
but  also  in  most  cases  ad' 

“ 2.  When  in  works  si 
parados  have  to  be  used,  well  sifted  earth  should  be  chosen 
in  preference  to  sand  in  l|ieir  construction.  Their  distance 

from  the  foot  of  the  interior 
le  end  of  the  gun  platform  should 
metres  (66  ft.)  if  the  work  is  ex- 
Ige  artillery  of  calibres  not  greater 
?s  than  thirty  metres  (99  ft.)  if  the 
powerful  artillery.  These  limits 
;ed  for  batteries  high  above  the  posi- 
Illery. 

“ 3.  As  the  inconvefiiences  resulting  from  parados  placed 
at  distances  less  than  miose  indicated  may  in  many  cases  be 
less  than  that  proceeding  from  the  fire  of  musketry  or  of 
artillery  placed  in  commanding  positions  in  rear  of  the  bat- 
tery, so  in  especial  cases  in  which  fortifications  have  to  be 
constructed,  the  irapoitance  of  the  two  dangers  will  have  to 
be  compared  in  order  to  judge  whether  it  is  better  to  place 
the  parados  at  less  diftance  or  to  expose  the  battery  to  re- 
verse fire.”  I 

203.  General  Rimarks.  The  methods  of  defilement 
here  laid  down  are  thqse  now  followed  by  engineers.  They 
unite  mathematical  accuracy  in  results  with  great  simpli- 
city of  detail ; and  rei|der  the  defilement  altogether  secon- 
dary to  the  other  conditions  of  defence,  upon  which  the 
plan  and  command  are?made  essentially  to  depend. 

Before  they  w’ere  adopted,  the  results  of  the  method  then 
followed  were,  in  most; respects,  like  those  obtained  in  the 
practical  operations  fo^  defiling  field  works.  A line  was 
taken,  the  position  of  which  was  determined  by  a series  of 
trials,  having  for  their  object  to  obtain  the  most  satisfactory 
8 


from  the  battery,  measu 
slope  of  the  parados  to 
be  not  less  than  twent; 
posed  to  the  fire  of  si( 
than  15  cm.  (6"),  nor 
work  is  exposed  to  m( 
may  be  somewhat  redi 
tion  of  the  attacking 


114 


ELEMENTS  OF  PERMANEN^T  FORTIFICATION. 


results  both  as  to  the  economy  of  the  requisit 
and  the  best  disposition  of  command  of  the  ' 
or  in  the  rear  of,  the  gorge  of  the  work  to 
position  coinciding  with  the  natural  surface, 
or  beneath  it  as  the  case  required.  Throi 
plane  was  passed  tangent  to  the  dangerous 


plane,  termed,  as  in  field  defilement,  a Ut  mjjant  Plane^ 


was  taken  as  the  artificial  site  of  the  work. 


I embankments 
arious  parts  at, 
)e  defiled  ; this 
or  being  above 
gh 


this  line  a 
ground.  This 


n reference  to 


which  the  relative  command  of  all  the  pans  was  arranged 
as  upon  a horizontal  site.  Or,  in  other  wirds,  the  result 
was  nearly  the  same  as  if  the  works  had  bee  i arranged  on  a 
horizontal  site,  and  then  the  whole  coml  ination  turned 
around  some  fixed  line  of  this  site,  until  it  w is  brought  into 
the  position  of  the  required  rampant  plane.  The  defects  of 
this  method  are  evident  at  a glance.  It  pi  eserves  the  re- 
lations of  defence  of  the  various  works  tlu  same  as  in  a 
horizontal  site  ; but  it,  to  a great  extent,  lea  ^es  out  of  con- 
sideration the  bearing  of  the  command  o i the  exterior 
ground,  and,  in  many  cases,  may  lead  to  e>  cessive  excava- 
tions and  embankments  which  the  method ! now  followed 
enable  the  engineer,  for  the  most  part,  to  av  fid. 

In  the  preceding  discussion  fixed  horizon  :al  limits  of  de- 
filade have  been  avoided,  as  they  must  be  determined  by 
considerations  of  relative  cost  and  value  to  ^e  defence. 

The  vertical  limit  is  considered  the  maximum  which  is 
practicable  or  generally  desirable.  It  is  f&ed  with  a view 
to  preventing  the  commander  of  a battery  feeing  the  effect 
of  his  own  shot  and  correcting  his  aim  |by  it.  It  is,  of 
course,  impracticable  to  prevent  the  effectlbeing  seen  from 
other  points ; but  when  many  guns  are  epgaged  this  is  of 
little  value  to  the  attack,  since  it  is  alm|st  impossible  to 
know  to  which  gun  any  single  shot  belong 

To  recapitulate : against  a plunging  fil’e  the  protection 
given  by  the  parapet  depends  only  up<|n  its  height  and 
the  angle  of  fall  of  the  projectile. 

fined  by  passing  a 
plane  with  the  proper  inclination  through  the  interior  crest 
witliout  considering  in  any  way  the  poir  t from  which  the 
shot  comes. 

Against  close  direct  fire  or  for  concealment  from  view, 
the  principles  and  problems  given  above  illustrate  the  meth- 
ods which  may  be  employed.  j 

To  what  extent  these  methods  shall  befused,  if  at  all,  will 
be  determined  by  the  circumstances  surrounding  each  par- 
ticular case.  I 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


115 


CHAPTEE  VIII. 

ACCESSORY  MEANS  OF  DEFENCE. 

I. 

204.  Water  may  be  made  a very  important  accessory 
means  of  defence  in  many  localities — as  in  a flat,  marshy 
country  where  the  level  of  the  natural  surface  lies  but  at 
a slight  elevation  above  the  water-level ; or,  as  in  the  case 
of  an  undulating  surface,  where  small  streams,  running 
through  valleys,  can  be  dammed  back,  so  as  to  produce  an 
inundation  of  some  extent. 

205.  In  the  former  case,  the  defensive  works  can  be 
easily  girdled  by  a zone  of  marshy  ground,  upon  which  it 
will  give  an  assailant  great  trouble  to  construct  his  trenches 
and  other  siege-works,  while  the  work  itself  can  be  secured 
from  attempts  at  surprise,  by  keeping  its  ditches  filled  with 
water  to  the  depth  of  six  feet  at  least.  In  such  a locality — 
moreover,  if  in  a climate  where  the  winters  are  mild — revetted 
scarps  and  counterscarps,  the  chief  use  of  which  is  to  pre- 
vent an  attempt  at  open  assault,  may  be  replaced  by  earthen 
ones,  a strong  stockade  being  formed  along  a wide  berm, 
answering  as  a corridor,  to  give  greater  security  on  the  more 
exposed  fronts  of  the  work. 

206.  In  the  latter  case,  portions  of  the  ground,  in  the 
immediate  vicinity  of  the  works,  may  be  covered  by  a sheet 
of  water,  of  sufficient  depth  to  prevent  their  being  used  by 
the  assailant  in  his  approaches;  and  within  the  inundation 
thus  artificially  produced  detached  works  may  be  erected, 
which,  having  flank  and  reverse  views  over  other  lines  of 
approach  of  the  assailant,  may  force  him  to  make  his  ap- 
proach upon  other  points  which  have  been  strongly  fortified 
to  meet  this  condition  of  things. 

To  form  these  artificial  inundations  the  locality  must  lend 
itself  to  the  construction  of  dams,  in  such  a position  that 
they  cannot  be  reached  by  the  assailant’s  missiles,  and  will 
be  secure  from  any  other  means  he  may  take  to  destroy 


116 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


them.  This  supposes,  then,  that  the  stream  should  either 
run  through  the  works,  so  that  the  dam  could  be  erected 
within  them,  or  so  near  to  them  that,  in  combination  with 
some  advanced  work,  the  dam  may  be  made  secure. 

In  a locality  having  these  features,  the  inundation  would, 
as  a general  rule,  have  to  be  formed  on  the  up-stream  side  of 
the  work,  since,  if  made  below  it,  the  dam  would  have  to  be 
placed  further  from  the  work,  and  the  inundation  itself 
might  spread  up  too  far  within.  Besides  these  objections 
to  this  position,  an  assailant  would  evidently  have  greater 
facilities  for  tapping  the  inundation  and  running  the  water 
off  than  when  it  occupies  the  up-stream  position. 

The  position  and  extent  of  the  dams,  and  the  other  neces- 
sary constructions  connected  with  them,  as  sluices,  waste 
weirs,  etc.,  will  depend  entirely  upon  the  local  features  of 
the  site,  and  will  form  a particular  study  in  each  case  for  the 
engineer. 

207.  Besides  these  uses  of  water  as  a passive  obstruction, 
arrangements  may  be  made,  when  the  locality  is  favorable 
to  it,  for  producing  a powerful  current  to  sweep  away  the 
assailant’s  works  in  the  ditches  by  letting  loose  a large  body 
of  water,  which  has  been  dammed  back  for  the  purpose, 
with  a rush  into  the  ditches.  This,  in  like  manner,  will  re- 
quire the  same  constructions  as  in  the ‘preceding  case,  and 
flash  gates  which  can  be  suddenly  turned  about  a horizontal 
or  a vertical  axis,  so  as  to  give  an  outlet  to  the  water  in  con- 
siderable volume  and  with  great  velocity.  These  gates  have 
to  be  placed  in  some  very  secure  point  of  the  ditches,  in- 
accessible to  the  assailant  and  covered  from  his  missiles,  and, 
if  effectively  used,  may  prove  a source  of  great  annoyanco 
to  him  by  frequently  frustrating  his  attempts  to  make  a 
passage  of  the  ditch. 

II. 

208.  Solid  hard  rock,  or  even  thin  layers  of  soft  rock 
alternating  with  layers  of  soil,  as  was  the  case  at  Sebastopol, 
are  great  obstructions  to  an  assailant’s  siege  works,  as  the 
rock  has,  in  many  cases,  to  be  blasted  out  to  gain  partial 
cover,  and  a large  amount  of  earth  with  trench  materials, 
has  to  be  brought  forward  at  great  risk  of  life  to  form  the 
parapets. 

In  constructing  a work,  nothing  should  be  omitted 
which,  if  placed  on  the  line  of  the  assailant’s  approaches, 
will  delay  his  operations  and  force  him  to  greater  efforts  and. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


117 


exposure.  To  this  end,  where  fragments  of  rock  can  be 
readily  had  in  sufficient  quantities,  it  should  be  used  in  form- 
ing the  embankments  of  the  glacis,  and  also  be  thrown  in 
upon  other  points,  over  which  important  lines  of  trenches 
must  necessarily  be  run.  ^ 

Besides  these  accessory  means  of  delaying  the  progress  of 
the  besieger’s  works,  a site  of  solid  rock  offers  the  further 
advantage  of  giving  natural  scarps  and  counterscarps,  where 
the  ditches  are  excavated  out  of  the  rock,  of  far  greater  re- 
sistance to  the  assailant’s  means  of  destruction  than  any 
masonry,  however  solidly  and  carefully  constructed,  can 
offer ; besides  forcing  the  assailant  to  construct  galleries 
through  the  rock  to  attain  the  level  of  the  bottom  of  the  ditch 
where  his  passage  of  it  is  to  be  constructed. 

209.  With  a similar  purpose,  the  stumps  of  large  trees 
may  be  left  in  like  positions,  and  trees  may  be  planted  when 
the  work  is  constructed  with  the  object  of  cutting  them 
down,  using  their  timber,  and  leaving  their  stumps  when  the 
work  is  threatened  with  a siege. 

210.  Obstacles  as  described  in  field  fortifications  may 
also  be  used  in  the  defence  of  a breach  or  as  an  aid  to  a weak 
scarp  wall,  for  which  they  are  even  recommended  by  some 
engineers  as  a substitute. 


III. 

211.  Mines,  when  properly  arranged  and  well  played, 
are  so  important  a defensive  means  that  they  should  con- 
stitute a part  of  the  permanent  dispositions  of  defence  of 
every  work  where  the  character  of  the  soil  will  admit  of  it, 
at  least  on  those  points  which  are  otherwise  weakest,  and 
therefore  most  liable  to  be  assailed. 

As  the  general  arrangement  of  a combination  of  galleries 
and  mine  chambers,  as  well  as  the  details  for  their  construc- 
tion, is  given  in  Military  Mining,  nothing  further  is  called 
for  here  than  to  state  that  the  principal  galleries  of  the 
combination  should  be  constructed  with  the  work,  and  of 
durable  materials,  leaving  the  other  parts  to  be  done  when 
the  exigency  calling  for  them  may  happen. 


118 


ELEMENTS  OF  PERMANENT  FORTIFICATION, 


CHAPTEE  IX. 

SEA-OOAST  DEFENCE. 

I. 

BATTERIES  ON  LAND. 

212.  The  different  character  of  the  attacks  to  which  sea- 
coast  and  interior  fortifications  are  subject,  leads  to  material 
differences  in  their  construction. 

The  guns  attacking  sea-coast  works  being  mounted  on 
ships  which  by  their  constant  movements  prevent  deliberate 
and  accurate  aim,  it  is  impossible  to  break  down  the  de- 
fensive works  by  placing  shot  after  shot  upon  a limited 
area,  as  is  done  by  breaching  batteries  on  land. 

On  the  other  hand  the  ships,  being  able  to  carry  the 
heaviest  guns,  can,  by  uniting  in  large  fieets  and  concentrat- 
ing their  fire  upon  one  or  two  works,  generally  have  the 
advantage  in  number  and  weight  of  guns  ; while  their  tops, 
presenting  poor  targets  to  the  defence,  are  particularly 
favorable  for  the  use  of  machine  guns  against  the  shore  bat- 
teries. 

213.  Stone  casemates,  which  as  previously  stated,  would, 
when  built,  stand  single  shots  from  the  heaviest  guns  then 
in  use,  are  now  easily  penetrated  and  the  fragments  of 
masonry  add  to  the  destruction  produced  by  the  projectile. 
Their  use  is  given  up  by  all  nations. 

Sea-coast  guns  are  now  protected  either  by  earth,  iron,  or 
steel. 

214.  Earthen  Batteries.  The  thickness  of  a sand 
parapet  equal  to  once  and  a half  the  penetration  of  the 
heaviest  shot  is  about  70  feet  (see  Table  of  Penetrations, 
Appendix  I).  This  thickness  is  excessive,  and  would  not  be 
often  used.  An  equal  resistance  with  a thinner  parapet 
may  be  obtained  by  using  concrete  or  large  blocks  of 
granite  set  in  cement,  the  resistance  of  the  first  being 
approximately  twice  and  of  the  second  three  times  that  of 
sand. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


119 


215.  As  before  remarked,  the  penetration  of  elongated 
projectiles  in  parapets  is  less  than  in  experimental  butts, 
and  the  result  of  the  bombardment  of  Alexandria,  in  1882, 
in  which  80-ton  guns  were  used,  led  to  the  conclusion  that 
“ No  English  gun  afloat  could  send  a projectile  through  or 
seriously  damage  a good  earthen  parapet  30  feet  in  thick- 
ness, at  ordinary  practicable  ranges.”  * 

216.  The  practice  in  Germany  is  to  make  earthen  para- 
pets of  sea-coast  works  from  33  to  40  feet  thick. 

The  tendency  of  American  engineers  is  to  use  thicker 
parapets. 

217.  No  matter  what  the  thickness  of  parapet,  a plung- 
ing shot  striking  near  the  interior  crest  generally  passes 
through  and  cuts  a furrow,  throwing  out  the  earth  and 
diminishing  the  height  of  the  parapet. 

This,  combined  with  the  plunging  Are  of  machine  guns 
from  the  ship’s  tops,  makes  it  necessary  to  give  the  greatest 
available  height  above  the  terre-plein  to  the  interior  crest  in 
open  batteries. 

This  height  of  interior  crest  is  of  little  value  if  the  gun, 
at  all  times,  and  its  detachment,  while  loading,  are  exposed 
to  the  Are  of  the  ship’s  cannon  and  machine  guns,  since  even 
the  smaller  cannon  can  by  a well  directed  shot  dismount  or 
disable  the  heaviest  gun,  or  the  machine  guns  sweep  away 
its  detachment. 

218.  Several  forms  of  disappearing  gun  carriages  have 
been  devised  which  allow  the  gun  to  be  lowered  behind  the 
parapet  to  load  and  to  be  raised  above  it  to  Are.  Figs.  2,  3, 
and  4,  Plate  7,  illustrate  three  of  these.  The  drawings 
show  their  general  features. 

219.  The  Moncrieff  works  well  for  the  smaller  guns  but 
is  not  applicable  to  the  larger  calibres. 

220.  The  Hydraulic  or  Hydro-pneumatic  requires  the 
use  of  steam  power  for  its  rapid  working,  but  it  may  be  ap- 
plied to  the  heaviest  guns  if  its  parts  are  properly  propor- 
tioned. 

221.  King’s  carriage  has  stood  the  test  of  exhaustive  ex- 
periments with  the  25-ton  gun,  may  be  worked  by  hand- 
power  with  a 50-ton,  and  if  properly  constructed  would 
work  with  the  100-ton  gun.  Major  King  proposes  with 
very  heavy  guns  the  use  of  hydraulic  pressure  instead  of 
hand-power  for  manoeuvring  the  carriage. 

*Note. — Report  of  British  Naval  and  Military  Operations  in  Egypt, 
1882,  by  Lieutenant-Commander  C.  F.  Goodrich,  U.  8,  Navy. 


120 


ELEMENTS  OE  PERMANENT  FORTIFICATION. 


222.  Open  batteries  exposed  to  slant  and  enfilade  fire 
must  be  protected  by  high  traverses  with  bonnets.  One,  or 
at  most  two,  guns  may  be  mounted  between  consecutive 
traverses. 

The  thickness  and  height  of  traverses  are  determined  by 
the  direction  of  the  fire  to  which  they  may  be  exposed. 

High  traverses  are  open  to  the  objection  that  they  show 
the  position  of  the  guns  to  the  enemy  at  great  distances. 

223.  When  the  battery  is  only  subject  to  front  fire,  the 
interior  crest  and  the  tops  of  the  splinter-proof  traverses 
should  be  held  in  the  same  plane. 

The  guns  should  be  painted  of  the  same  color  as  the  para 
pet  or  background  and  provided  with  shields  to  protect  the 
guTiners  from  small  projectiles. 

224.  Powder  magazines  and  shell  rooms  are  made  under 
the  traverses  communicating  by  a lift  with  the  loading 
passage  in  the  traverse  at  the  level  of  the  terre-plein  and 
generally  close  to  the  interior  slope,  the  gun  being  traversed 
so  that  it  is  presented  at  this  passage  for  loading.  Plate  7, 
Fig.  1. 

A bomb-proof  room  for  the  relief  detachment  is  also  built 
in  the  traverse. 

When  hydraulic  power  is  used,  bomb-proof  shelters  for 
the  steam  boilers  and  pumps  are  built  in  a place  secure  from 
hostile  fire. 

225.  When  placed  upon  a commanding  plateau,  of  ample 
area,  the  battery  may  consist  of  a series  of  gun-pits  sunk  in 
the  earth  and  fitted  up  as  previously  described. 

226.  This  construction  is  particularly  well  suited  for 
mortar  batteries,  which  may  be  set  back  from  the  crest  of 
the  height,  the  pits  being  made  to  contain  from  one  to  four 
mortars  each ; the  traverses  between  the  pits  serving  for 
magazines,  shell-rooms,  cover  for  the  men,  and  firing  points 
for  the  groups  of  mortars,  which  may  be  placed  very  close 
together  and  fired  from  tlie  shelter  provided. 

Plate  2 is  a battery  for  12  mortars  designed  by  Gen.  H. 
L.  Abbot,  Corps  of  Engineers,  described  in  Ho.  XI.  Printed 
Papers  Essayons  Club,  March  3,  1869. 

227.  The  increased  accuracy  of  fire  and  weight  of  pro- 
jectile of  the  rifled  mortars  has  given  them  much  greater 
value  for  use  against  ships,  and  will  cause  them  to  be  ex- 
tensively used  in  the  defence  of  channels  and  anchorages. 
Their  fire  attacks  a ship  upon  its  flat  deck,  which,  is  its  most 
vulnerable  part  above  water.  They  can  be  silenced  neither 
by  the  ship’s  cannons,  machine  guns,  nor  mortars  on  float- 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


121 


TRg  structures.  Mortar  batteries  are  not  expensive  either 
in  construction  or  armament. 

228.  If  the  site  of  a battery  be  very  high,  100  feet  or 
more  above  the  water,  it  is  generally  considered  that  guns 
mounted  on  simple  barbette  or  embrasure  carriages  in  open 
batteries  will  be  able  to  hold  their  own  against  ships,  owing 
to  the  difficulty  which  the  latter  experience  in  working  their 
heavy  guns  at  high  elevations,  and  the  loss  of  plunge  in  the 
fire  of  the  machine  guns.  In  this  case,  however,  as  in  the 
low  batteries,  the  guns  should  be  provided  with  shields 
against  small  projectiles  and  the  cannoniers  should  be 
covered  with  a sufficient  height  of  parapet. 

229.  The  Use  of  Armor.  Where  the  sites  are  con- 
tracted, earthen  batteries  cannot  be  built,  and  when  vrithout 
considerable  command  open  batteries  are  rendered  unten- 
able by  the  small  arms  and  machine  guns  of  the  ships.  For 
these  sites  covered  defences  of  iron  or  steel  are  alone  avail- 
able. 

These  are  either  casemates  or  turrets ; they  are  made  of 
wrought-iron,  compound-plates,  steel  or  chilled  cast-iron. 

when  a limited  field  of  fire  only  is  desired,  casemates 
have  the  advantage  of  cheapness,  but  usually  require  a some- 
what larger  embrasure,  which  as  well  as  the  muzzle  of  the 
gun  is  constantly  exposed  to  hostile  fire. 

Turrets  give  an  all-round  fire  with  the  smallest  possible 
embrasure  and  almost  complete  protection  so  long  as  the 
armor  is  not  pierced,  and  allow  the  muzzles  of  the  guns  to 
be  turned  to  the  rear  while  loading. 

They  are  more  expensive  than  casemates  in  themselves, 
in  their  substructure  and  in  the  machinery  for  their  working. 

230.  The  great  expense  of  iron  and  steel  constructions 
will  always  limit  their  application  to  the  protection  of  guns 
of  the  highest  power,  which  cover  important  points.  The 
smaller  guns  will  generally  be  placed  in  open  batteries. 
These  smaller  guns  being  much  cheaper  in  themselves,  their 
mounting  and  emplacements,  as  well  as  much  more  rapid  in 
their  fire,  which  is  nearly  as  effective  as  that  of  the  large 
guns  against  unarmored  ships  and  the  unprotected  parts  of 
iron-clads,  they  should  be  provided  in  as  large  numbers  as 
practicable. 

II. 

231.  Floating  Batteries.  In  some  harbors  of  large 
area  or  with  marshy  banks,  emplacements  for  guns  com- 
manding the  channels  cannot  be  obtained  on  shore. 


122 


ELEMENTS  OF  PEKMANENT  FORTIFICATION. 


For  these  cases  the  defence  will  sometimes  require  float- 
ing armored  batteries  , of  small  speed,  light  draught,  and 
great  thickness  of  arnto^,  which  may  be  placed  in  differ- 
ent points  of  the  harbor  passing  over  shoals  to  avoid  being 
rammed,  or  to  pass  from  one  channel  to  another  when  de- 
sired. They  will  carry  the  heaviest  guns  with  the  best  pos- 
sible protection,  and  not  being  designed  to  go  to  sea,  can  be 
made  stronger  in  guns  and  armor  than  the  attacking  ships. 
Their  flrst  cost  and  the  constant  expense  of  keeping  them 
in  serviceable  condition  prohibits  their  use  except  in  harbors,, 
which  can  be  defended  in  no  other  way. 

III. 

232.  Obstacles,  Submarine  Mines  and  Torpedoes. 

The  defence  of  harbors  is  not  possible  without  the  use  of  a 
sufficient  number  of  guns  and  mortars ; but  where  the  in- 
ducement is  great  enough  to  justify  it,  or  the  inner  harbor 
is  not  well  protected,  vessels  can,  and,  under  favoring  circum- 
stances will,  run  by  the  outer  batteries,  however  well  con- 
structed and  armed,  unless  obstacles,  passive  or  active,  are 
placed  in  the  channels  which  will  hold  them  under  the  fire 
of  the  guns  until  they  are  disabled  by  this  fire  or  by  the 
action  of  the  obstacles  themselves. 

A perfect  defence  requires,  beside  guns  and  mortars, 
passive  obstacles  and  submarine  mines  or  torpedoes. 

233.  Obstacles.  The  following  general  conditions 
should  be  fulfilled  by  a system  of  passive  obstacles,  viz. : 

1st.  They  should  be  in  readiness  for  use  at  short  notice, 
and  of  such  simple  construction  as  to  be  readily  placed  in 
position  by  river  and  harbor  tug-boats. 

2d.  They  should  be  capable  of  withstanding  the  effects  of 
currents  and  storms,  and  the  action  of  marine  insects  and 
growths  for  a considerable  time. 

3d.  They  should  either  be  so  strong  and  rigid  as  to  break 
through  the  bottoms  of  vessels  striking  them,  or,  if  of  a 
yielding  character,  their  resistance  should  gradually  increase 
until  it  stops  a vessel  coming  against  them. 

4th.  They  should  be  so  placed  as  to  be  thoroughly  swept 
by  the  fire  of  both  the  large  and  small  guns  of  the  defence, 
and  of  a construction  which  will  not  be  seriously  injured  by 
this  or  the  hostile  fire. 

234.  The  passive  obstacles  generally  used,  and  which 
satisfy  the  above  conditions  to  a greater  or  less  degree,  de- 
pending upon  their  construction,  the  character  of  the  bot- 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


123 


tom,  the  currents,  the  temperature  of  the  water  and  their 
expense,  are  sunken  vessels  and  cribs,  piles  driven  and 
rigidly  braced  in  a vertical  or  inclined  position ; piles 
driven  nearly  to  the  bottom  with  .floating  and  pointed  logs 
attached  to  them  by  chains,  making  artificial  “ sawyers 
booms  and  rafts  stretched  across  the  channel ; floating  nets 
of  chains,  wire  or  other  rope  supported  by  buoys  and  gen- 
erally carrying  ropes  with  loose  ends  to  become  entangled  in 
the  wheels  of  attacking  vessels ; and  in  shallow  water  che- 
vaux  defrise  or  any  other  extemporized  devices. 

Of  these  the  fixed  obstructions  can  be  used  only  in  chan- 
nels intended  to  be  closed  somewhat  permanently ; the  float- 
ing ones  being  used  in  those  which  it  may  be  necessary  to 
open  for  the  passage  of  friendly  vessels. 

235.  Submarine  Mines  and  Torpedoes.  Subma- 
rine mines  and  torpedoes  were  first  tried  in  the  war  of  the 
Revolution,  but  hardly  passed  the  experimental  stage.  They 
were  again  used  in  the  Crimean  war  to  a very  limited  ex- 
tent. 

Their  flrst  successful  application  on  a comparatively  large 
scale  was  in  the  war  of  Secession,  1861-5. 

236.  K system  of  submarine  mines  to  be  efficient  should 
satisfy  the  following  conditions,  viz.  : 

1st.  The  positions  which  they  are  to  occupy  should  be 
selected,  all  parts  of  the  permanent  structures  designed  for 
their  use  prepared,  and  all  the  mines  and  their  attachments 
provided,  properly  marked  and  stored  during  peace. 

2d.  The  mines  should  be  as  strong,  cheap,  and  simple,  as 
is  consistent  with  efficiency. 

3d.  They  should,  when  used,  be  planted  in  multiple  lines 
or  groups  so  disposed  as  to  close  the  channels ; and  their 
electrical  connections  should  be  so  made  that  a limited  num- 
ber of  cables  being  cut  by  enemy  will  not  disable  the  mines 
in  such  a way  as  to  open  a channel  through  the  lines. 

4th.  The  lines  and  groups  must  be  thoroughly  swept  by 
the  fire  of  the  large  and  small  guns  of  the  defence. 

5th.  Trained  officers  and  men  in  sufficient  number  to 
place  and  work  the  mines  must  be  always  available. 

237.  Fixed  torpedoes,  known  as  submarine  mines,  serve 
to  close  the  channel  to  hostile  vessels  while  leaving  it  open 
to  those  of  the  defence. 

Movable  torpedoes,  known  as  torpedoes^'’  may  be  used 
to  harass  the  enemy  either  at  anchor  or  in  motion. 

Torpedo  boats  of  small  size  and  great  speed,  using  spar 
torpedoes  or  more  frequently  launching  “ auto  mohiles^'^  of 


124 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


the  Whitehead  type,  may  move  out  from  the  harbors  and 
attack  the  fleet  at  distances  entirely  beyond  cannon-range 
and  even  in  the  open  sea. 

238.  These  torpedo  boats  and  floating  batteries  are  con- 
necting links  between  the  defence  by  land  and  sea  forces. 

239.  Submarine  mines  are  either  self-igniting  or  con- 
trolled from  the  shore.  The  self-acting,  once  placed,  close 
the  channels  equally  to  friend  and  foe.  Those  controlled 
from  the  shore  by  electricity  may  at  will  be  made  active 
against  hostile,  or  harmless  toward  friendly  vessels. 

The  latter  class  only  can  be  employed  in  harbors  which 
are  to  be  used  for  naval  or  commercial  purposes. 

240.  Submarine  mines  of  both  kinds  are  either  ‘‘  buoy- 
ant” or  “ ground.” 

The  latter  rest  on  the  bottom,  and  may  be  used  in  water 
not  exceeding  40  feet  in  depth  ; the  former  in  deeper 
water,  being  held  in  place  by  an  anchor  and  a cable  which 
hold  them  at  the  proper  depth  below  the  surface. 

241.  The  buoyant  self-acting  mines  are  exploded  by  the 
contact  of  a vessel  wdth  the  mine  itself ; the  ground  mines 
by  contact  with  the  buoy,  the  explosion  being  caused  by 
the  action  of  a very  sensitive  fuse. 

242.  In  mines  controlled  from  the  shore,  the  buoyant 
mine  itself  and  the  buoy  attached  to  the  ground-mine  carry 
a “ circuit-closer”  (or  breaker)  which,  acting  under  the  shock 
caused  by  the  vessel  striking  them,  either  announces  the 
contact  to  the  operator  in  the  electrical  room,  or  fires  the 
mine  as  may  be  desired.  Ip  some  cases  they  are  tired  only 
by  the  action  of  the  operatoi,  the  position  of  the  vessel  with 
reference  to  them  being  determined  by  observers  on  shore. 

243.  The  details  of  the  circuit-closers,  annunciators  and 
arrangements  for  firing  the  mines  differ  materially  in  dif- 
ferent nations,  and  are  taught  in  their  special  schools.  An 
attempt  is  generally  made  to  keep  them  concealed  from 
other  nations. 

They  necessarily  are  more  or  less  complicated  and  deli- 
cate in  their  construction  and  adjustment,  and  require  for 
their  effective  use  operators  skilled  in  electricity,  familiar 
with  delicate  mechanisms,  and  of  careful  and  non-excitable 
disposition,  assisted  by  trained  and  reliable  men. 

244.  That  system  is  best  which  is  designed  to  fulfil  only 
the  necessary  requirements  with  the  least  possible  complica- 
tion of  parts,  and  in  which  the  parts  are  as  simple,  strong, 
easily  accessible,  and  easily  understood  by  simple  inspection, 
as  possible. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


125 


In  addition  to  this,  the  electrical  connections  of  the  dif- 
ferent parts  should,  so  far  as  practicable,  be  permanently 
made  by  the  manufacturer,  leaving  to  the  operator  only  the 
necessity  of  attaching  the  torpedo  wires  and  batteries  for 
testing  and  firing. 

245-  The  requisites  for  the  satisfactory  working  of  the 
electrical  system  are  that  each  mine  and  cable  may  be  tested 
as  to  its  condition,  that  contact  with  a mine  must  be  sig- 
nalled ; and  that  any  mine  may  be  fired  by  the  operator, 
whether  it  has  or  has  not  been  struck  by  a passing  vessel. 

The  electric  connection  between  the  mines  and  the  oper- 
ating-room is  by  insulated  cables  of  the  kind  used  for  sub- 
marine telegraphs. 

246.  The  cases  of  ground-mines  may  be  of  cast-iron  of  a 
hemispherical  or  similar  shape,  as  are  the  anchors  of  the 
buoyant  mines. 

247.  The  cases  of  the  buoyant  mines  in  our  service  are 
made  of  mild  steel  of  spherical  shape.  They  have  a volume 
which  gives  them  sufficient  buoyancy  to  sustain  their  own 
weight,  that  of  the  charge  and  mooring  cable,  and  enough 
excess  to  prevent  them  from  being  too  much  depressed  in 
depth  by  the  action  of  the  currents  of  the  place  where  they 
are  to  be  used. 

248.  They  are  charged  with  the  most  powerful  explosive 
attainable  which  is  safe  to  handle,  and  not  liable  to  be  in- 
jured by  age  or  moisture.  Gun  cotton,  dynamite  and  ex- 
plosive gelatine,  are  the  principal  explosives  now  used. 

249.  Movable  Torpedoes  include,  1st.  The  “auto- 
mobile” or  self-propelling,  of  which  the  Whitehead  and 
Howell  are  examples.  They  contain  their  own  motive 
power,  generally  compressed  air,  and  once  launched,  no 
further  control  can  be  exercised  over  them.  2d.  The  “ fish 
torpedoes”  of  which  the  Lay  and  Simms  are  examples. 
Tliey  are  driven  by  liquid  carbonic  acid  and  an  electric 
motor  respectively,  and  are  directed  by  electricity  through 
cables  which  they  reel  out  as  they  run.  Their  effective 
range  is  about  two  miles.  3d.  Drifting  torpedoes,  which  float 
with  the  current  and  are  intended  to  explode  upon  striking  a 
vessel.  4th.  Submarine  boats  designed  to  pass  under  a 
vessel,  fix  a mine  to  it.  and  retire  before  the  explosion 
occurs.  A description  of  these  different  torpedoes  does  not 
properly  belong  to  the  subject  of  fortifications. 

250.  The  destructive  range  of  submarine  explosions 
being  very  limited,  every  effort  is  made  to  cause  them  to 
take  place  as  near  the  vessel  attacked  as  possible. 


12(5 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


The  law  of  diminution  of  pressure  and  kinetic  energy,  in 
the  transmission  of  the  shock  from  subaqueous  explosions 
of  the  principal  explosive  compounds  has  been  well  deter- 
mined by  General  Abbot  and  published  in  Professional 
Papers,  Corps  of  Engineers,  U.  8.  A.,  No.  23,  1881.” 

The  resistance  of  modern  vessels  to  these  shocks  is  not  so 
well  known,  and  can  only  be  determined  by  many  costly 
experiments,  comparatively  few  of  which  have  yet  been 
made. 

251.  Organization  of  Fortifications,  Mines,  and 
Torpedoes  for  the  Defence  of  Harbors.  The  tor- 
pedo boats  working  out  beyond  cannon-range  form  the 
first  line  of  defence.  When  driven  in,  they  retreat  until 
covered  by  the  forts,  and  come  into  action  again  if  oppor- 
tunity offers. 

252.  The  fish  torpedoes  come  into  play  about  two  miles 
from  shore.  They  have  not  yet  had  the  test  of  actual  use 
in  war. 

253.  The  forts  and  submarine  mines  arranged  in  defen- 
sive relations  form  the  main  line  of  defence  upon  which  the 
safety  of  the  harbor  will  usually  depend. 

254.  Submarine  mines  derive  a moral  effect  from  the 
destruction  which  is  worked  by  a single  one  successfully 
exploded,  which  prohibits  the  passage  of  the  hostile  fleet 
until  the  mines  are  destroyed  or  rendered  inert.  To  render 
them  harmless  the  enemy  must  capture  the  fortifications 
covering  the  operating  rooms,  cut  all  the  cables,  destroy 
the  mines  by  blowing  them  up  with  counter  mines,  or 
disable  them  by  grappling  and  dragging. 

That  these  operations  could  be  carried  on  by  ships  or 
boats  in  narrow  channels  under  the  close,  well-directed  fire 
of  powerful  guns,  and  the  action  of  movable  torpedoes,  and 
of  the  mines  themselves,  is,  if  not  absolutely  impossible,  of 
evident  improbability.  It  may  be  said  that  a harbor  pro- 
vided with  an  efficient  torpedo  defence,  thoroughly  supported 
by  both  large  and  small  guns,  is  practically  impregnable  by 
naval  attack. 

If,  however,  the  supporting  guns  are  not  covered  by  forti- 
fications strong  enough  to  enable  them  to  hold  their  own 
against  the  heaviest  ship’s  guns,  they  may  be  silenced  and 
captured,  and  with  their  fall  the  torpedo  defence  falls  also, 
as  it  is  manifest  that  the  torpedo  defence  can  have  no 
value  whatever  when  the  control  of  its  firing  arrangements 
falls  into  hostile  hands. 

255.  The  possibility  that  the  enemy  may  break  through 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


12? 


•a  single  or  even  double  line  of  mines  by  sacrificing  one  or 
two  ships,  by  well-worked  counter-mines,  by  cutting,  one  or 
two  groups  of  cables  by  a fortunate  shot,  or  by  the  occur- 
rence of  one  of  the  many  accidents  which  may  disable  some- 
what delicate  electrical  apparatus,  makes  it  necessary  that 
the  third  condition  above  given,  should  be  fulfilled. 

256.  Remarks.  The  more  modern  and  better-developed 
•systems  of  submarine  mines  as  harbor  defences  have  not  as 
yet  stood  the  test  of  actual  attack.  In  all  the  wars  which 
have  occurred,  since  their  development,  their  moral  effect 
has  deterred  naval  commanders  from  assailing  harbors  de- 
fended by  forts  and  supposed  to  be  supplied  with  a system 
of  submarine  mines. 


ELEMENTS  OE  PERMANENT  EORTIEICATION, 


CHAPTER  X. 

THE  DEFENSIVE  ORGANIZATION  OF  FRONTIERS  WITH 
PERMANENT  FORTIFICATIONS. 

257.  Xo  State,  in  the  present  condition  of  civilization, 
can  be  regarded  as  secure  from  foreign  military  aggression, 
the  accessible  points  of  whose  frontiers  are  not  occupied  by 
permanent  fortifications  of  such  strength  as  shall  prevent 
an  enemy  from  obtaining  possession  of  them  by  a sudden 
assault,  and  thus  procuring  the  means  of  penetrating  into 
the  interior.  Guided  by  the  experience  of  centuries  of 
wxars,  and  the  daily  increasing  facilities  which  the  improve- 
ment in  the  materiel  of  armies  and  their  transportation 
afford  for  rapid  and  powerful  offensive  operations,  the 
ruling  states  of  Continental  Europe  have,  within  the  last 
half-century,  not  only  made  every  effort  to  place  their  fron- 
tiers in  an  unassailable  condition,  but  also  their  great  centres 
of  population  and  wealth  in  the  interior,  beyond  the  chances 
of  a sudden  attack  from  an  enemy  who  might  force  his 
way  through  the  frontier  defences  and  march  rapidly  upon 
them,  thus  making  these  positions  the  rallying  points  where 
a defeated  army  can  find  a safe  resting-place  until  it  can  be 
reorganized  and  sufficiently  strengthened  to  resume  the 
offensive. 

Such  seems  to  be  the  result  at  which  the  generals  and 
statesmen  of  Europe  have  arrived,  after  the  most  mature 
and  careful  consideration  of  the  important  problem  of  na- 
tional defence ; at  a time  when  the  utility  of  ijermanent 
fortifications  loas  seriously  called,  in  question^  by  some 
who  pointed,  in  support  of  their  views,  to  the  very  ineffi- 
cient part  the  great  nuipber  of  fortified  places  had  played 
in  the  wars  waged  by  Napoleon,  when,  by  means  of  over- 
whelming numbers  in  the  field,  he  was  enabled  to  disregard 
such  places,  the  garrisons  of  which  were  too  feeble  to  make 
any  efficient  offensive  movements,  until  the  defeat  of  his 
adversary,  in  one  or  more  great  pitched  battles,  necessariljr 
also  threw  them  into  his  possession. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


129 


In  view  of  the  arguments  based  on  tliese  events,  the 
opinions  of  Napoleon  himself  should  carry  great  weight. 
In  speaking  of  the  bearing  of  permanent  fortifications  in  a 
defensive  war,  he  says : “ If  fortresses  can  neither  secure  a 
victory,  nor  arrest  the  progress  of  a conquering  enemy,  they 
can  at  least  retard  it,  and  thus  give  to  the  defence  the 
means  of  gaining  time — a most  important  advantage  in  all 
warfare.”  In  like  manner  the  Archduke  Charles  of  Austria, 
who  showed  himself  one  of  the  ablest  adversaries  with 
whom  Napoleon  was  called  upon  to  cope,  took  the  ground 

that  a defensive  warfare  cannot  be  systematically  and 
successfully  carried  on  in  a country  which  is  not  provided 
with  fortresses  that  have  been  planned  and  distributed 
according  to  strategical  requirements.”  Like  views  were 
held  by  the  Duke  of  Wellington;  and  it  is  probable  that 
no  great  general,  from  the  earliest  period  of  military  opera- 
tions down  to  the  present  moment,  has  ever  entertained  the 
contrary. 

Without  going  further  back  than  the  Franco-Prussian  war 
of  1870-71,  we  find  that  while  the  entrance  of  the  German 
army  upon  French  territory  was  easily  accomplished,  owing 
to  its  superiority  in  numbers,  organization,  and  rapid 
mobilization  at  the  first  stage  of  the  war,  it  was  necessary 
to  detach  from  the  advancing  army  the  large  forces  invest- 
ing Metz,  Strasburg,  Belfort,  and  other  fortified  places. 

These  forces,  with  their  artillery,  were  occupied  from  30 
to  100  days  in  reducing  these  strong  places,  whicli  were  upon 
their  lines  of  communication  and  could  not  be  neglected. 

The  fortifications  of  Paris,  although  their  scarp  walls  were 
exposed  and  their  casemates  not  strong  enough  to  resist  the 
German  artillery,  held  the  German  army  in  check  from  the 
middle  of  September  until  the  end  of  January,  affording 
four  and  one  half  months  for  the  organization  of  an  army  of 
relief  in  the  other  parts  of  France. 

The  fact  that  this  opportunity  was  not  made  use  of  has  no 
bearing  upon  the  value  of  the  fortifications,  which  more 
than  fulfilled  their  original  design. 

That  this  value  was  appreciated  by  both  sides,  is  shown 
in  the  immense  sums  spent  by  them  since  that  time  in  build- 
ing new  forts  and  remodelling  the  old.  The  only  question, 
then,  on  this  subject  that  remains  for  solution  by  a State  is, 
in  what  way  such  a means  of  security  from  aggression  can 
be  best  adapted  to  its  own  geographical,  political,  and  mili- 
tary status. 

258.  In  a country  like  our  own,  with  so  vast  an  extent 
9 


130 


ELEMENTS  OF  PEKMANENT  FORTIFICATION. 


of  sea-coast  and  inland  frontier,  and  with  political  and  social 
institutions  which  are  so  antagonistic  to  every  approach  to 
a large  standing  army  as  a measure  of  national  safety,  this 
question  is  one  of  peculiar  importance,  both  from  the  open 
character  of  this  extensive  frontier,  and  from  the  almost 
incredible  facility  with  which  considerable  armies,  with  all 
their  materiel^  can  be  concentrated  on  distant  points  by  the 
aid  of  steam.  The  weakness  of  our  immediate  neighbors  on 
the  one  side,  and  the  daily  increasing  mutual  commercial 
interests  between  us  and  the  greatest  naval  power  in  the 
world,  by  which  we  might  be  seriously  threatened  both 
along  our  seaboard  and  our  extensive  line  of  inland  frontier, 
it  is  true,  would  seem  to  favor  the  hope  that  the  day  is  still 
remote,  and  from  present  appearances,  may  never  arrive,  in 
which  our  country  will  have  to  apprehend  anything  in  the 
shape  of  invasion  except  along  the  sea-coast ; and  we  may, 
therefore,  dismiss  from  our  consideration  any  other  pro- 
vision against  this  eventuality  (which,  should  it  happen, 
looking  to  our  resources  in  men  and  means,  wull  hardly  ex- 
tend inland  beyond  a few  marches),  except  what  we  have 
already  attempted,  viz.,  the  securing  of  our  principal  har- 
bors, naval  stations,  and  commercial  marts  from  a naval 
attack,  or  from  one  combined  with  the  operations  of  a land 
force,  which,  from  the  causes  above  alluded  to,  could  be  but 
of  short  duration. 

259.  In  the  organization  of  the  inland  frontier  fortifica- 
tions of  a state,  the  points  to  be  princi})ally  regarded  are  the 
principal  avenues  of  access  to  it,  and  their  topographical 
features  as  they  lend  themselves  more  or  less  to  strengthen 
the  artificial  defences.  In  conducting  an  invasion  across  an 
inland  frontier,  the  march  of  the  enemy  must  necessarily  be 
along  the  roads  that  intersect  it,  as  these  afford  the  only 
means  for  transporting  the  materiel^  etc.,  of  the  army.  The 
points,  therefore,  or  places  in  their  neighborhood  where  the 
principal  roads  or  other  avenues  of  communication  cross  the 
frontier,  particularly  those  which  lead  to  the  great  centres 
of  population  and  wealth,  are  the  ones  which  would  neces- 
sarily call  for  permanent  defences.  No  absolute  rule  can  be 
laid  down  for  the  distribution  and  strength  of  such  works 
along  a frontier.  Everything  must  depend  upon  the  greater 
or  less  of  facility  presented  to  an  enemy  for  penetrating  at 
one  point  rather  than  another,  and  upon  the  ulterior  advan- 
tages the  one  may  present  to  him  over  another. 

260.  Rivers  and  mountain  ranges  are  the  natural  fortifi- 
cations of  states;  and  where  they  form  the  frontiers  they 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


13l 


greatly  facilitate  the  application  of  artificial  defensive 
mean^  as  they  present  but  few^  and  those  in  general  im- 
portant, points  of  access. 

When  these  points  on  a river  are  fortified,  an  invading 
force,  however  powerful,  cannot,  without  great  risk,  cross 
the  river  without  first  gaining  possession  of  them ; for,  even 
should  a sufiicient  detachment  be  left  to  observe  and  block- 
ade the  fortresses,  the  main  army,  in  case  of  retreat  or  any 
disaster,  might  be  placed  in  an  extremely  critical  position, 
in  its  movements  to  recross  the  river,  with  the  garrisons  of 
the  fortresses  threatening  its  fianks  and  rear. 

261.  In  offensive  operations,  fortresses  upon  a river  fron- 
tier form  one  of  the  strongest  bases  of  operations.  If  a 
river  intersects  the  frontier,  the  point  where  it  crosses  it,  or 
some  one  in  its  vicinity,  should  be  occupied  by  a permanent 
work ; among  such  points  those  are  more  peculiarly  neces- 
sary to  be  held  where  a river  forming  the  frontier  is  inter- 
sected by  another  navigable  one  which  lies  wholly  within 
the  frontier. 

The  importance  of  thoroughly  occupying  such  points  is 
ol)vious,  as  they  afford  an  army  on  the  defensive  the  means 
of  passing  readily  and  safely  from  one  side  to  the  other  of 
the  river,  either  to  evade  a force  too  powerful  for  it  to  cope 
with  in  the  open  field,  or,  when  an  opportunity  offers,  from 
any  imprudent  movement  of  an  invading  force  on  one  side, 
to  throw  itself  suddenly  from  the  other  on  its  flank  or  rear, 
and  thus  force  it  to  a retrograde  movement. 

262.  With  respect  to  mountain  passes,  the  main  roads 
alone  will  require  permanent  works.  If  the  passes  are  in- 
dependent of  each  other,  a work  will  be  necessary  for  each 
one  separately ; bnt  where  several  unite  at  the  same  point, 
upon  or  within  the  frontier,  a single  work  placed  upon  this 
point  will  suffice.  Local  circumstances  will  determine  the 
point  in  each  pass  which,  occupied,  will  offer  the  greatest 
advantage  for  obstructing  the  march  of  an  invading  force 
and  retarding  the  hringmg  forward  its  materiel.  The  only 
rule  that  can  be  given  is  that,  while  the  position  selected 
shall  satisfy  these  conditions,  there  shall  be  every  facility  of 
communication  between  the  fortress  and  the  interior  for  re- 
ceiving supplies  and  reinforcements.  This  rule  would  lead 
generally  to  the  selection  of  some  point  of  the  outlet  within 
the  frontier  as  the  pr  oper  one. 

263.  The  number  of  fine  natural  harbors  and  roadsteads 
on  our  seaboard,  where  the  largest  fleets  can  find  a secure 
anchorage  at  all  seasons ; the  proximity  to  the  ocean  of 


132 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


many  of  our  most  important  cities,  towns,  and  popnlons 
villages,  by  which  they  are  not  only  exposed  to  the  usual 
dangers  of  naval  attacks,  but  to  incursions  from  an  enemy’s 
land  forces;  together  with  the  large  rivers  which,  having 
their  outlets  on  this  seaboard  frontier,  are  navigable  for  long 
distances  within  it  by  vessels  of  the  greatest  Inirden — have 
given  to  the  subject  of  sea-coast  defences  a particular  prom- 
inence among  ourselves. 

The  means  of  defence  disposable  for  the  security  of  such 
points  consists  in  permanent  works  arranged  to  meet  an 
attack  both  by  sea  and  land,  and  of  such  strength  as  the 
presumed  nature  of  the  attack  will  demand ; of  such  tem- 
porary fortifications  as  the  exigency  of  the  moment  may 
point  out ; of  movable  land  forces  ; and  of  fioating  defences 
to  act  in  aid  of  the  others. 

264.  The  character  of  the  permanent  defences  will  de- 
pend upon  the  object  in  view.  Where  this  is  simply  to* 
exclude  an  enemy’s  fieet  from  the  use  of  a harbor  or  road- 
stead, which  olfers  to  him  no  other  inducement  for  its  occu- 
pation but  that  afforded  by  a secure  anchorage,  one  or  more 
small  works  of  sufficient  strength  to  prevent  the  success  of 
an  open  assault  upon  them,  armed  with  heavy  mortars  and 
guns  with  long  ranges,  that  can  reach  by  their  fire  every 
point  where  an  enemy’s  ship  could  safely  anchor,  will  be 
sufficient. 

The  points  to  be  occupied  by  these  works,  as  well  as  their 
plan,  will  depend  upon  the  natural  features  of  the  harbor 
or  roadstead  itself. 

They  will  usually  consist  either  of  open  works  with  guns 
in  barbette  and  mortars  sweeping  all  points  of  approach  to 
and  within  the  harbor  ; or  of  a combination  of  covered  and 
barbette  batteries ; with  ditches  or  other  obstacles,  and  ' 
bomb-proof  barracks  of  sufficient  capacity  to  hold  the  gar- 
rison necessary  to  beat  ofi  an  open  assault  on  the  battery  by 
land,  and  to  be  secure  from  a conjhde-main. 

Like  defences  will  also  be  sufficient  for  the  security  of  the 
smaller  classes  of  towns  and  villages,  which  would  probably 
offer  a temptation  only  to  a small  naval  force. 

265.  In  the  case  of  important  commercial  cities  and  large 
naval  depots  lying  within  harbors  more  or  less  accessible 
both  to  sea  and  land  attacks,  the  character  of  the  defences 
called  for  must  necessarily  be  commensurate  with  the  magni- 
tude of  the  interests  to  be  guarded,  and  the  consequent 
temptation  to  an  enemy  to  put  forth  great  efforts  for  thc-iw 
occupation  and  destruction. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


133 


The  avenues  of  approach  to  these  objects  by  sea,  which 
can  be  brought  within  range  of  cannon  and  mortars  in  forti 
fications  on  the  shore,  or  in  armored  forts  erected  on  natural 
or  artificial  islands,  should  be  occupied  to  a distance  that 
will  prevent  a fleet  from  approaching  near  enough  to  open 
a bombardment,  and  if  practicable  also  force  the  enemy,  if 
he  ventures  a land  attack,  to  disembark  his  forces  either  at 
so  great  a distance  from  the  object  to  be  reached  that  he  will 
not  be  able,  by  a sudden  movement  of  this  nature,  to  effect 
a surprise  ; or  to  limit  his  landing  to  such  points  on  the 
coast  as,  from  their  exposed  position,  may  render  the 
cooperation  of  the  naval  and  land  forces  very  uncertain, 
and,  in  case  of  a storm,  place  the  latter  in  a very  perilous 
condition  if  attacked. 

These  works  will  form  the  exterior  chain  of  the  defences. 
Within  these,  batteries,  either  open  or  casemated,  as  the 
locality  may  seem  to  demand,  should  occupy  all  the  most 
suitable  positions  for  sweeping  the  path  that  a fleet  must 
follow  by  powerful  cross,  direct,  and  enfilading  fires,  and 
for  reaching  every  point  of  anchorage  within  the  harbor. 

The  batteries  commanding  the  inner  harbor  within  easy 
Tange  of  the  city  have  especial  value  in  attacking  and  de- 
stroying, by  their  cross-fire,  any  ships  which  might  run  past 
the  outer  forts.  The  presence  of  such  batteries  will  prob- 
ably deter  the  ships  from  attempting  this  kind  of  attack. 

On  the  land  approaches,  points  should  be  occupied  by 
forts  of  a permanent  character,  which  wdll  prevent  a suffi- 
ciently near  approach  to  bombard  the  city  or  depot,  and, 
in  combination  with  temporary  works,  will  afford  an  in- 
trenched field  of  battle  for  the  troops  on  the  defensive. 
These  will  form  the  exterior  line  of  the  land  defences,  the 
interior  line  being  either  a continuous  enceinte  strong 
enough  to  resist  assault,  or  else  a suitable  combination  of 
either  continuous  or  detached  field  works  of  such  strength 
and  armament  that  the  enemy,  in  any  attempt  to  carry  them 
by  an  open  assault,  will  be  made  to  suffer  heavily,  even  if 
he  is  not  repulsed. 

The  security  of  objects  of  this  character  will  be  greatly 
increased  when  they  lie  at  some  distance  within  the  sea- 
coast  frontier,  and  can  only  be  approached  by  water  through 
such  comparatively  narrow  defiles  as  even  onr  largest  rivers 
present,  and  by  land  after  one  or  more  marches.  These 
defiles  will,  for  the  most  part,  not  only  present  admirable 
positions  on  their  banks  from  which  an  assailant’s  fleet  can 
be  enfiladed  within  the  range  of  the  heaviest  guns,  but 


134 


ELEMENTS  OF  PERMANENT  FORTIFICATION, 


frequently  others,  at  points  where  the  river  narrows,  or 
changes  its  course,  where  works  occupying  the  opposite 
banks  will  give  the  means  of  rendering  the  river  impass- 
able by  torpedoes,  booms,  rafts,  or  other  floating  and  sunken 
obstructions,  which  cannot  be  removed  except  by  getting 
possession  by  a land  attack  of  the  defences  which  guard 
them. 

266.  Wherever  harbors  or  bays  are  of  such  extent  that 
their  entrance  cannot  be  interdicted  to  an  enemy’s  fleet,  nor 
secure  anchorage  within  them  be  prevented,  of  which  we 
have  examples  on  our  own  coast,  the  case  falls  beyond  the 
province  of  fortification,  and  must  be  left  to  floating  de- 
fences for  a solution.  Here  even  some  fortified  harbors  on 
the  shores  of  such  extensive  estuaries  may  give  secure  places 
of  refuge  for  ships-of-war,  from  which  they  may  at  any 
moment  sally  when  they  can  take  the  enemy  at  a disadvan- 
tage, or  into  which  they  can  retreat  if  attacked  by  a supe- 
rior force. 

267.  In  the  great  military  states  of  Continental  Europe, 
the  question  as  to  what  extent  the  great  centres  of  popula- 
tion and  wealth  in  the  interior  should  be  covered  by  fortifica- 
tions, has  been  submitted  to  the  investigation  of  the  alflest 
engineers  and  statesmen,  from  the  time  of  Yauban  down  to 
the  present  day ; but  more  particularly  since  the  fall  of 
Hapoleon,  a catastrophe  which  might  not  have  taken  place 
had  Paris  been  secured  by  fortifications  which  would  have 
prevented  a coujp- de-main^  when  the  armies  of  the  Allies 
gained  possession  of  it  as  the  result  of  a pitched  battle. 
Whatever  differences  of  opinion  have  been  called  forth  as 
to  the  mode  of  accomplishing  this  object,  as  shown  in  the 
published  views  on  the  proposition  to  fortify  Paris,  there 
seems  to  have  been  none  among  those  best  qualified  to  de- 
cide upon  it  as  to  the  great  importance  of  so  fortifying  this 
capital  and  other  large  places  in  the  interior,  as  Lyons,  etc., 
which  from  their  position  must  be  of  the  highest  strategical 
value  in  the  case  of  a successful  invasion  by  a large  army,  as 
not  only  to  prevent  their  wealth  and  resources  from  falling 
into  the  possession  of  the  invading  force,  but  to  make  them 
safe  rallying-points  for  beaten  and  dispersed  forces,  and 
depots  for  organizing  new  armies. 

The  plan  that  has  been  adopted  for  this  end,  both  in 
France  and  in  most  of  the  other  cities  of  Europe  which  have 
been  either  newly  fortified  or  had  their  old  work  strength- 
ened within  this  period,  is  to  surround  the  city  by  a con- 
tinuous enceinte  of  greater  or  less  strength.  y>ut  one  secure 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


135 


from  a coup-de-main^  and  to  occupy  with  forts  of  a per- 
manent character  the  most  suitable  points  in  advance  of  the 
enceinte,  to  prevent  an  enemy  from  bombarding  the  city,  or 
penetrating  between  them  without  first  gaining  possession 
of  them.  By  this  plan,  it  is  proposed  to  gain  all  the  advan- 
tages offered  by  the  passive  resistance  of  fortifications  and 
the  activity  of  a disposable  movable  force  occupying  the  zone  . 
between  the  enceinte  and  the  forts  as  an  intrenched  camp, 
upon  which  the  forts  and  temporary  works  thrown  up  be- 
tween them  would  render  an  open  assault  too  perilous  to 
be  attempted. 

268.  The  fortifications  of  Paris,  of  1840,  consist  of  a 
continuous  bastioned  enceinte,  without  outworks,  with  a 
revetted  scarp  of  the  usual  height,  to  secure  it  from  esca- 
lade, and  a ditch  with  a counterscarp  of  earth.  The  ad- 
vanced forts  are  either  quadrangular  or  pentagonal  bas- 
tioned works,  inclosing  all  the  means  of  security  for  their 
garrisons,  as  bomb-proofs,  etc.,  their  plan  being  skilfully 
adapted  to  the  site,  and  their  mutual  bearing  on  the  defence. 

After  the  siege  of  1870-71,  these  fortifications  were  in- 
creased by  the  addition  of  an  exterior  line  of  forts  occupy- 
ing the  outer  crest  of  the  basin  of  Paris  approximately  upon 
the  circumference  of  a circle  of  24  miles  diameter,  that  of 
the  inner  belt  being  about  12  miles  and  the  enceinte  about 
6 miles. 

The  new  detached  forts  are  polygonal  without  outworks. 

The  fortifications  of  Lyons  present  more  diversity,  both 
in  the  plan  and  details  of  the  enceinte  and  forts ; although 
the  general  system  is  the  same  as  that  of  Paris.  There  is 
here  seen  a more  extensive  application  of  casemated  and  gal- 
lery defences,  both  for  exterior  flanking  and  for  the  defence 
of  the  interior  forts,  growing  out  of  the  more  broken  feat- 
ures of  the  site  generally,  and  frequently  the  more  confined 
space  occupied  by  them. 

In  Germany  the  same  general  system  of  a continuous 
enceinte,  with  strong  advanced  isolated  works,  has  been 
followed ; the  whole  being  so  planned  and  combined  as  to 
meet  the  distinctive  features  of  what  is  known  as  the  Ger- 
man system  of  fortification.  The  principal  changes  in  those 
have  already  been  described. 

269.  In  our  own  country,  where  the  important  centres  of 
population  and  wealth  lie  almost  immediately  upon  the  sea- 
board, it  would  seem  impracticable,  in  view  of  the  rapid 
spread  of  population  around  them,  and  the  consequent 
changes  in  local  features,  to  resort  to  any  defences  of  a per- 


13G 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


manent  character  to  secure  them  from  a land  attack,  even 
were  the  nation  willing  to  assume  the  burden  of  the  great 
outlay  for  such  an  object ; as,  in  a few  years,  the  works  of 
to-day  might  be  rendered  useless  by  the  changes  referred 
to.  Even  in  Europe,  the  strongest  despotic  governments 
have  been  obliged  to  cede  what  seemed  military  exigencies 
to  the  demands  of  the  social  condition ; and  either  to  raze 
the  fortifications  of  cities,  to  give  room  to  a crowded  popu- 
lation, or  else  to  suffer  such  encroachments  on  the  ground 
necessary  for  their  action  as  to  render  them  nearly  useless. 
The  only  defensive  resource  that  seems  left  to  ourselves,  in 
like  cases,  is  in  the  use  of  field-works — one  which  our  mili- 
tary experience  shows  may  be  relied  upon  with  confidence, 
so  long  as  the  military  aptitude  of  our  population  remains 
unchanged  from  what  it  has  thus  far  proved  itself  to  be. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


137 


% 

CKAPTEE  XL 

SUMMARY  OF  THE  PROGRESS  AND  CHANGES  OF 
FORTIFICATION. 


I. 


270.  The  records  of  history  ind  the  vestiges  of  remote 
civilization  show  that  the  art  of  :mrtification,  in  some  guise 
or  another,  has  been  in  practice  tl^oughout  all  nations,  even 
in  the  lowest  stages  of  social  progi  3ss  ; and  that,  wherever  it 
has  been  cultivated,  its  character  las  been  more  or  less  in- 
fluenced, not  only  by  the  natural  features  of  the  country, 
but  b}"  the  political  and  social  coni  litions  of  its  inhabitants. 

In  its  earliest  applications,  we  f nd  men  resorting  to  one 
or  more  simple  enclosures  of  ea  ’then  walls ; or  of  these 
surmounted  by  stakes  placed  in  ji  xtaposition  ; or  of  stakes 
alone  flrmly  planted  in  the  grour  d,  wnth  a strong  wattling 
between  them ; or  of  timber  in  it  3 natural  state,  having  its 
branches  and  the  undergrowth  st  ongly  interlaced  to  form 
an  impervious  obstruction,  with  ortuous  paths  through  it 
only  known  to  the  defenders. 

A resort  to  such  feeble  means  i hows  not  only  a very  low 
state  of  this  branch  of  the  militai  y art,  but  also  of  that  of 
the  attack  ; as  defence  of  this  1 ind  would  present  but  a 
slight  obstacle,  except  against  an  e lemy  whose  habitual  mode 
of  fighting  was  as  cavalry,  or  ag  linst  one  not  yet  conver- 
sant with  the  ordinary  plans  for  s caling.  This  class  of  for- 
tifications for  the  defence  of  entir  j frontiers  has  been  mostly 
met  with  in  the  east  of  Europe, 
time,  found  to  be  a sufficient 
nomadic  tribes  that  for  ages  h 

plains,  and  who  are  only  formidable  as  a mounted  force. 

271.  To  secure  greater  perntnence  and  strength,  the 
next  step  was  to  form  walls  eith 
alone,  or  of  these  intermixed 
trees.  Obstructions  of  this  kin 
limited  extent,  and  were  confines 


and  was  doubtless,  at  the 


protection 
ve  roamed  over 


against 


those 
its  vast 


jr  of  rough  blocks  of  stone 
nth  the  trunks  of  heavy 
could  only  be  used  to  a 
to  the  defences  of  places 


138 


ELEMENTS  OF  PERMAl^ENT  FORTIFICiLTIOK. 


forming  the  early  centres  of  population.  fAs  human  in^ 
vention  was  developed,  these,  in  their  turn,  were  found  to 
present  no  serious  obstacle  to  an  assault  by  escalade;  giving 
to  the  assailed  only  the  temporary  advaiAage  of  a more 
commanding  position ; and  they  gave  pfece  to  walls  of 
dressed  stone,  or  brick,  whose  height  and  perpendicular  face 
alike  bade  defiance  to  individual  attemptslto  climb  them,  or 
the  combined  effort  of  an  escalade.  Froni  the  tops  of  these 
inaccessible  heights,  sheltered  in  front  by  parapet  of  stone, 
and,  in  some  cases,  by  a covered  cor  rid  oif  behind  them,  the 
assailed  could  readily  keep  at  bay  any  enimy,  so  long  as  he 
was  exposed  to  their  missiles ; but  Mving  reached  the* 
foot  of  the  wall,  he  here  found  shelter  :^om  these,  and,  by 
procuring  any  cover  that  would  protects  him  from  objects 
thrown  from  above,  could  securely  work  it  effecting  a breach 
by  mining.  It  was  probably  to  remedy  fins  defect  of  simple 
walls  that  towers,  wFich  at  first  were  |:iothing  more  than 
square  or  semicircular  projections  built,  from  distance  to  dis- 
tance, in  the  wall  itself,  were  first  devised  ; and  which  sub- 
sequently w^ere  not  only  enclosed  thrcLghout,  but  divided 
into  stories,  each  of  which  was  provided  with  loop-holes,  to 
flank  the  adjacent  towers  and  the  stra|ght  portions  of  the 
wall  between  them.  Each  tower  coul(|  be  isolated  from  the 
straight  portion  of  the  walls  adjacenf  to  it,  by  an  inter- 
ruption at  the  top  of  the  wall,  over  wh|ch  a communication 
between  the  tower  and  wall  could  be  |stablished  by  a tem- 
porary bridge.  i 

272.  These  formidable  defences  wer|,  in  their  turn,  found 
to  be  insufficient  against  the  ingenuity  and  skill  of  the  as- 
sailant, who,  by  means  of  covered  gallj'ies  of  timber,  some- 
times above  ground  and  sometimes  befieath,  gradually  won 
his  way  to  the  foot  of  the  wall,  where,?by  breaking  his  way 
through  it,  or  by  undermining  and  supporting  it  on  timber 
props  to  be  subsequently  destroyed  by  fire,  he  removed  the 
sole  obstruction  to  a bodily  collision  with  the  assailed. 

These  methods  of  assault  were  in  some  cases  supported  by 
means  of  high  mounds  of  earth  whicff  w^ere  raised  in  an  in- 
clined plane  towards  the  walls,  and  sometimes  carried  forward 
to  them,  from  the  top  of  which  the  assailant,  by  the  erection 
of  wooden  towers,  covered  with  raw  hides  to  secure  them 
from  being  burnt,  could  command  the  interior,  and,  driving 
the  assailed  from  the  walls,  gain  a foothold  on  them  by 
lowering  a drawbridge  from  the  wooden  tower. 

273.  These  changes  in  the  attack  led  to  new  modifica- 
tions in  the  defence,  which  consisted  in  surrounding  the 


ELEMENTS  OF  PERMANENT  FORl^IFICATION.  1^50 

/ 

/ 

place  by  wide  and  deep  ditches,  of  \^liich  the  walls  formed 
the  scarp,  the  counterscarp  being  eirfer  of  earth  or  revetted. 
This  placed  a formidable  obstacle  p the  mode  of  attack  by 
mining,  and  also  to  the  use  of  eartpen  mounds,  as  these  last 
had  to  be  constructed  across  the  gptch  before  they  could  gain 
sufficient  proximity  to  the  wall^ither  to  form  a com  muni 
cation  with  its  top,  or  to  breachit  by  means  of  the  battering- 
ram  ; the  ditches  also  were  htfed  with  water  whenever  this 
obstruction  could  be  procurectf  and  when  dry  they  formed  a 
defile  through  which  the  ass^led  often  sallied  upon  the  as- 
sailant with  success  when  f<^nd  at  a disadvantage  in  it. 

274.  The  gigantic  prol^  often  given  to  the  fortifica- 

sions  of  antiquity  seems  ^nost  incredible,  as  well  as  their 
extent.  In  many  cases  a Jbuble  wall  of  stone  or  brick  was 
filled  in  between  with  earih,  forming  a wide  rampart  upon 
which  several  vehicles*  cottld  go  abreast.  Not  only  was  the 
space  enclosed  by  some  m these  fortifications  that  requisite 
for  the  habitations,  but  ground  enough  was  taken  in  to  add 
considerably  to  the  foo(f  of  the  inhabitants  and  cattle,  for 
the  long  periods  to  wlfich  blockades  were  in  many  cases 
extended,  when  all  oth|r  means  of  reducing  the  place  had 
failed.  | 

The  wall  built  by  th|  Eomans,  between  Carlisle  and  New- 
castle, to  restrain  the  incursions  of  the  Piets  into  the  south- 
ern portions  of  the  isiaiid,  was  seventy-three  miles  in  extent, 
about  twelve  feet  in  hfight,  and  nine  feet  in  thickness.  The 
extent  and  dimension^  of  this  work  sink  almost  into  insig- 
nificance when  compaiied  with  those  of  the  celebrated  wall  of 
China,  built  to  restraip  the  incursions  of  the  Tartars.  This 
structure  is  about  llOO  English  miles  in  length  ; has  a 
height  of  27  feet ; itsihickness  at  top  is  11  feet.  The  lower 
portion  of  it  is  builtf  of  dressed  stone,  the  upper  of  well- 
burned  brick.  It  is  tanked  at  distances  of  about  80  yards 
apart  by  towers  in  which  iron  cannon  are  found. 

In  the  great  extentiit  embraces,  it  necessarily  crosses  hills 
and  valleys,  and  in  ^many  places  important  defiles.  An 
examination  of  its  paits  has  shown  that  in  its  plan  there  was 
an  evident  design  to  ddapt  it  to  those  features  of  its  site,  as 
it  is  well  thrown  bacl^  to  the  rear  of  difficult  passes  ; and  at 
points  where  there  is  most  danger  to  be  apprehended 
from  attempts  of  invasion,  there  are  several  walls  in  suc- 
cession. 

275.  The  mode  of  attack  of  fortified  places  resorted  to 
by  the  ancients  was  reduced  to  settled  rules,  and  brought  to 


140 


ELEMENTS  OE  PERMANENT  /FORTIFICATION. 


the  highest  state  of  perfection  the  Greeks,  about  the 
epoch  of  Alexander  the  Great  aiK^  the  immediate  successors 
to  his  vast  conquests.  An  essential  feature  in  it,  whether 
in  the  sieges  of  inland  fortresse^^or  those  on  the  seaboard, 
was  to  cut  off  all  communicatior/ between  the  place  and  the 
exterior,  by  hemming  it  in  by  ^a  and  land,  with  stationary 
forces,  covered  themselves  by  lir/’es  of  intrenchments  strength- 
ened by  towers,  and,  in  the  ca^'e  of  sea-coast  places,  also  by 
fleets,  from  all  assaults  both/ from  without  and  from  the 
place  invested. 

Having  selected  the  portions  of  the  place  on  which  the 
attack  was  to  be  directed,  a ^econd  line  was  formed  parallel 
to  the  flrst,  which  was  covered,  and  constructed  of  timber 
and  wicker-work,  and  secui^d  with  raw  hides  to  prevent  its 
being  set  on  fire.  From/ this  sheltered  position,  which 
served  also  the  purposes  of  a lodging  for  the  besiegers,  the 
besieged  were  annoyed  with  missiles  thrown  from  all  the 
artillery  known  in  that  dajq  consisting  of  the  ordinary  bow, 
the  cross-bow,  and  the  yarious  machines  for  projecting 
heavy  stones  and  other  projectiles. 

Under  the  diversion  tljus  made,  the  besiegers  pushed  for- 
ward from  this  line  several  covered  approaches  of  a like 
construction  directly  upon  the  place,  for  the  purpose  of 
gaining  the  counterscarp  of  the  place,  and  from  that  posi- 
tion filling  up  the  ditch  with  stones,  earth,  heavy  logs,  etc., 
to  prepare  the  way  for  placing  the  battering-ram  in  position 
to  breach  the  wall.  The  tower  in  which  this  machine  was 
placed  usually  consisted  of  several  stories,  and  was  occupied 
by  troops  who  cleared  The  top  of  the  wall  assailed  of  the 
besieged.  This  operation  was  frequently  aided  by  other 
high  towers,  which  we|e  advanced  either  along  the  natural 
level  of  the  ground,  oi|  upon  artificial  mounds  forming  in- 
clined planes,  towards'  the  place,  by  means  of  which  the 
towers  could  be  given  any  desirable  command  over  the  in- 
terior. 

276.  The  defence  was  mostly  of  a passive  character  ; the 
besieged  trusting  mainly  to  the  strength  of  their  defences, 
under  cover  of  which  they  resorted  to  all  the  means  used  by 
the  besiegers  for  assailing  the  latter  when  they  came  within 
reach  of  their  missiles ; using  cranes  and  other  devices  to 
seize  upon  the  implements  planted  at  the  foot  of  the  wall, 
and  carrying  out  galleries  of  countermines  to  overwhelm 
the  artificial  mounds  and  their  towers. 

277.  The  Homans  evinced  their  decided  military  apti- 
tude, not  only  in  the  employment  of  the  ordinary  systematic 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


141 


methods  of  the  attack  and  defence  of  fortified  places,  but  in 
their  application  of  the  cardinal  principle  of  mutual  defen- 
sive relations  between  the  parts  of  a fortified  position,  ob- 
tained by  advanced  and  retired  portions  of  the  enceinte; 
and  also  in  the  adaptation  of  intrench  men ts  to  the  natural 
features  of  the  site,  as  shown  in  the  fortifications  of  some  of 
the  permanent  frontier  camps  of  their  military  colonies. 
These  principles  have  also  been  noticed  in  some  of  the  for- 
tified positions  of  India,  which  consist  of  a mural  enceinte 
with  the  earthen  ramparts  flanked  by  round  towers,  and  of 
round  towers  in  advance  of  the  enceinte  connected  with  it 
by  caponnieres. 

With  the  decadence  of  the  Roman  Empire,  the  art  of 
fortification,  like  the  other  branches  of  the  military  art,  was 
brought  to  so  low  a stage  that  strongholds  whicli,  skilfully 
defended  with  energy,  would  have  baffled  the  efforts  of  a 
well-trained  assailant  in  the  art  of  attack,  fell,  almost  with- 
out resistance,  into  the  possession  of  the  fierce  northern 
hordes,  by  which  the  whole  of  civilized  Europe  was  over- 
run. ^ 

278.  The  remains  of  the  structures  raised  for  defensive 
purposes,  during  the  prosperous  days  of  the  Empire,  were 
probably  the  sole  means  of  protection  afforded  to  the  inhab- 
itants of  the  towns  that  still  maintained  a nucleus  of  popu- 
lation, until  the  rise  of  the  Western  Empire,  under  Charle- 
magne ; and  it  was  the  necessity  felt  by  this  conqueror,  not 
only  of  securing  his  conquests,  but  of  checking  the  irrup- 
tions of  the  barbarous  tribes  along  his  extended  frontier, 
which  led  him  |o  erect  tetes-de-jpont  on  the  frontier  rivers, 
and  a line  of  strpng  towers,  for  garrisons  of  a few  men,  upon 
the  most  inaccessible  and  prominent  points  of  this  frontier ; 
the  latter  being 'a  means  which  was  subsequently  resorted  to 
for  a like  purpose  in  the  Spanish  peninsula. 

Henry  I.,  of  Germany,  introduced  a more  important  and 
more  systematic  addition  to  these  permanent  frontier  de- 
fences, by  surrounding  the  frontier  towns  and  villages,  occu 
pied  by  militaryl  colonists,  with  walls  and  ditches,  to  secure 
them  from  suchi  attacks  as  they  might  be  exposed  to,  and 
subsequently  adding  a second  line  of  strongholds  within  the 
frontier,  by  whiiph  an  irruption  through  the  frontier  line 
might  still  be  checked. 

279.  During  the  general  disorganization  of  States  under 
the  feudal  system,  the  free  cities  wfflich  depended  for  their 
defence  on  the  burghers  composing  the  different  crafts, 
every  individual  who  could  maintain  a few  retainers  in  his 


142  ELEMENTS  OF  PERMANENT  FORTIFICATION. 

pay,  and  the  clergy,  even,  resorted— ^ach  according  to  their 
separate  views — to  such  means  of  Jiefence  as  would  best 
secure  them  from  the  attacks  of  osiers  in  a like  condition, 
and  would  enable  them  to  carry  o^t  that  system  of  pillage 
which  had  become  general  amongst  the  nobles  and  other 
military  chieftains.  I 

280.  From  this  state  of  society  sprang  up  those  castles, 

placed  in  the  most  inaccessible  /positions  on  the  lines  of 
communication  which  the  little  inland  commerce  that  was 
still  carried  on  was  obliged  to  ^Taverse.  These  were  pro- 
vided with  every  possible  device  for  an  obstinate  passive 
defence,  being  surrounded  by  ^ wide  and  deep  ditch,  or 
moat,  over  which  a drawbridge-  was  the  only  communica- 
tion to  the  main  entrance,  whicfh  was  flanked  by  towers  on 
the  exterior,  and  closed  with  massive  doors ; the  tortuous 
passage  which  led  from  them  fto  the  interior  of  the  castle 
being  further  secured  by  a grated  portcullis,  which  could 
be  let  drop  at  a moment’s  | notice,  to  arrest  a sudden 
assault.  f 

To  these  means  were  often-  joined,  besides  the  ordinary 
measures  of  loop-holes  and  machicoulis  in  the  walls  and 
towers  for  annoying  the  assailant,  a high  interior  tower, 
termed  a keep,  or  donjon,  which,  commanding  the  exterior 
defences,  was  also  a watch-tower  over  the  adjacent 
country. 

The  keep,  which  was  the  last  defensible  point,  was,  in 
Bome  cases,  provided  with  a secret  subterranean  passage, 
having  its  outlet  in  some  distant  concealed  spot,  through 
which  succor  could  be  introduced  into  the  beleaguered 
castle  ; and,  in  the  last  extremity,  the  garrison  find  safety  in 
a stealthy  flight.  ! 

281.  The  fortifications  of  towns  partook  of  the  same 
characteristics  as  those  of  castles.  From  the  custom  of 
assigning  to  the  different  burgher  crafts,  each  of  which  had 
an  independent  military  organization,  the  exclusive  guard- 
ianship of  portions  of  the  enceinte,  as  well  as  their  erection 
and  repairs,  great  diversity,  and  frequently  a whimsicality, 
in  the  defensive  arrangements  was  the  natural  result ; the 
evidence  of  which  still  exists  in  the  remains  of  the  walls  of 
some  of  the  old  Continenial  cities.  The  art,  for  the  most 
part,  was  practised  by  ambulatory  engineers,  who,  like  the 
secret  orders  by  whom  the  bridges  and  churches  of  the 
same  period  were  built,  offered  their  services  wherever  they 
were  \vanted.  Many  ideas  were  also  introduced  from  the 
East  by  the  Crusaders,  as  exhibited  in  the  fortifications  of 


I 


ELEMEi^'TS  OF  PERMANENT  FORTIFICATION.  ^^3 

castles  and  cities  belonging  to  the  Templars  and  other  re- 
ligions military  orders. 

282.  With  the  invention  of  gunpowder,  and  its  applica- 

tion to  military  purposes,  a gradual  revolution  took  place 
in  the  general  forms  and  details  of  fortification.  It  was 
soon  seen  that  naked  walls  alone  did  not  offer  either  suit- 
able conveniences  for  the  new  military  machines,  or  suffi- 
cient protection  against  the  projectiles  thrown  from  them. 
This  led  to  the  introduction  of  earthen  ramparts  and  para- 
pets, which  were  placed  against  the  walls  and  suitably 
arranged  to  meet  the  exigencies  of  the  moment.  The  art 
received  something  like  a scientific  basis  about  this  time  in 
Italy,  from  w-hich  the  names  and  forms  of  n-ost  of  the 
elements  of  fortification  now  in  use  are  derived.  The  Italian 
engineers,  like  their  ;^redecessors,  went  from  state  to  state 
to  offer  their  services  wherever  they  were  needed,  and  in 
this  way  disseminated  the  principles  of  their  school  through- 
out Europe.  | 

283.  It  was  at  tms  epoch  that  the  bastioned  form  of  for- 
tification first  appeared,  but  the  precise  date  and  the  author 
of  the  invention  are  both  unknown.  With  its  introduction 
the  importance  of  separating  the  parts  of  a line  of  fortifica- 
tion into  advancedfand  retired  parts,  the  latter  fianking  and 
defending  the  fori|ier,  seems  to  have  been  recognized  as  an 
essential  principle  of  the  art.  With  these  changes  in  the 
form  of  the  ence|nte,  the  art  was  gradually  improved  by 
the  addition  of  (^tworks  to  increase  the  amount  of  cross 
and  flank  fire ; th|  introduction  of  bomb-proof  shelters  for 
the  troops  and  oper  purposes ; the  substitution  of  earthen 
for  stone  parapets ; and  the  attempt  to  conceal  the  scarp 
walls  from  the  enemy’s  batteries  by  decreasing  the  command 
and  deepening  tl|e  ditches  of  the  enceinte. 

By  these  gradual  changes  stone  walls,  which  in  the  old 
fortifications  we|*e  the  essential  defensive  features,  came  at 
length  to  be  regarded  in  their  true  character,  sim])ly  as  pas- 
sive obstacles  to|an  open  assault  by  escalade.  The  property 
of  earthen  parapets,  of  resisting  without  material  loss  of 
strength  the  long-continued  fire  of  the  assailant’s  heaviest 
guns,  showed  that  the  same  defensive  means  were  applica- 
ble both  to  wmrks  of  a permanent  and  of  a temporary  char- 
acter ; and  were  equally  available  for  the  purposes  of  the 
assailant  and  the  assailed.  The  measures  for  the  attack  and 
the  defence  of  positions  were  thus  reduced  to  the  same  gen- 
eral principles,  differing  only  in  the  forms  and  dimensions 
of  the  elementary  parts,  as  circumstances  seemed  to  demand. 


/ 


ELEMP]NTS  OF  PERiilANB^T  FORTIFICATION. 


i44 

284.  Italian  School.  above  stated,  the  first  em- 
ployment of  bastions  as  they  now  exist  was  made  by  the 
Italian  engineers;  and,  as  far  as  has  been  ascertained, 
towards  the  close  of  the  fift^nth  or  the  commencement  of 
the  sixteenth  century.  To  whom  the  credit  of  their  inven- 
tion is  due  is  not  known.  4n  the  earlier  fronts  of  the  Italian 
school  the  bastions  are  ve^ry  small,  and  they  are  connected 
by  curtains  varying  from^^SO  to  500  yards  in  length.  The ' 
bastion  fianks,  which  w^re  perpendicular  to  the  curtains, 
were  divided  into  two  portions ; that  next  to  the  curtain, 
which  was  one-third  o|'^the  entire  flank,  was  thrown  back 
and  covered  by  the  potion  in  advance,  which  thus  formed 
what  received  the  nan|e  of  the  orillon.  The  lower  part  of 
the  retired  portion  wis  casemated  for  cannon  ; and  behind 
this,  and  separated  from  it  by  a dry  ditch,  rose  a second 
flank,  having  the  same  command  as  the  other  parts  ot*  the 
enceinte  parapet.  |n  some  cases  a small  and  very  obtuse 
bastion  was  erected ^^t  the  middle  of  long  curtains. 

The  ditches  of  the  enceinte  were  usually  about  100  feet, 
wide  and  24  feet  dieep ; the  counterscarps  being  parallel  to 
the  bastion -faces. 

A scarp  gallery|  for  the  purpose  of  mining,  ran  through- 
out the  enceintel  scarp,  and  communicated  with  galleries 
leading  to  other  points. 

The  parapets,  at  first  of  masonry,  were  afterwards  of  earth, 
and  from  18  to  ^4  feet  thick.  The  earth  of  the  rampart 
was  sustained  oh  the  interior  by  a wall.  Eamps  estab- 
lished a commu|iication  between  the  interior  and  the  ram- 
part. 

The  defects  of  these  early  fronts  were  soon  felt,  and  a 
more  complicated  but  improved  method  adopted,  in  which 
the  bastions  wore  enlarged  and  the  curtains  diminished. 
The  retired  flanks  were  still  retained,  but  the  orillon  instead 
of  being  angular  was  rounded.  To  these  improvements, 
cavaliers  were  Sometimes  added  to  the  bastions,  which  in 
those  cases  were  made  witliout  retired  flanks  ; or  placed  on 
the  curtains,  when,  from  the  configuration  of  the  site,  some 
portion  of  the  ground  within  cannon-range  could  not  be 
swept  from  the  enceinte  parapet.  The  covered-way  was 
introduced  and  became  an  integral  part  of  the  front ; and  a 
small  demi-lune  or  ravelin  was  placed  in  advance  of  the 
enceinte  ditch,  forming  a tke-de-pont  to  cover  the  commu- 
nication, at  the  middle  of  the  curtain  across  the  main  ditch, 
between  the  enceinte  and  the  exterior.  The  covered-way, 


ELEMENTS  OF  PERMAN  NT  FORTIFICATION. 


145 


width  and  bordered  the  main 
s subsequently  provided  with 


which  at  first  was  of  nnifoi 
/id  demi-lune  ditches, 
salient  and  reentering  pla^s-of-arms.  These  various  essen- 
tial parts  of  a fortified  frjmt  were  gradually  ameliorated  bv 
the  Italian  engineers,  b#  not  before  the  Italian  school  had 
left  its  impress  upon  fortification  of  all  the  other  states 
of  Europe;  as  the  I^ian  engineers,  from  their  superior 
acquirements,  were  i^demand  throughout  these  states. 

285.  Spanish  S;0iool.  From  the  existing  fortifications 
of  Spain,  the  infiue^e  of  the  Italian  school  may  be  traced, 
but  modified  by  Ational  characteristics ; the  works  seem 
organized  more  f#  a purely  passive  defence  ; the  covered- 
way, that  essenti^  outwork  to  an  active  defence,  being  in 
many  cases  omitftd  ; the  means  of  annoying  the  besiegers 
by  tires  being  gfeatly  multiplied ; and  the  outworks  gen- 
erally being  arringed  with  a view  to  a purely  passive  de- 
fence. BesidesI  this,  the  dimensions  of  the  profile  and 
height  of  scarp/were  increased  as  a greater  security  against 
escalade  ; inteifor  retrenchments  were  multiplied,  sometimes 
enclosing  a bfmb-proof  keep  to  render  the  defence  more 
obstinate.  | 

The  Spani^i’ds,  although  resorting  but  little  to  sorties, 
show  great  sl#ll  and  pertinacity  in  the  defence  of  breaches, 
and  in  availing  themselves  of  all  obstructions  for  prolonging 
resistance.  | 

From  theibroken  character  of  many  of  the  sites  of  their 
fortresses,  tile  Spaniards  resorted  very  much  also  to  detach- 
ed works  t(j  occupy  commanding  points  from  which  the 
main  work  could  be  annoyed. 

These  th|y  also  generally  organized  for  a strictly  passive 
defence,  le^ing  them  more  to  their  own  resources  than  to 
any  cooperation  with  the  main  work. 

286.  Di  tch  School.  This  school  took  its  rise  in  the 
political  ne  iessities  of  the  times,  in  which  the  national  spirit 
was  aroLisq  i to  throw  off  an  onerous  foreign  yoke.  The 
aquatic  clu  racter  of  the  country,  and  the  want  of  time  and 
pecuniary  neans,  led  to  those  expedients  of  defence  which 
are  never  ranting  under  like  circumstances.  The  deficiency 
of  earth  lell  to  the  formation  of  low  parapets  for  the  main 
enceinte  apd  wide  ditches  filled  with  water.  The  main 
enceinte  ^^jas  usually  preceded  by  a second  one  with  a very 
low  para|:^t  to  sweep  the  surface  of  the  wet  ditch  ; and 
this  seconq  enceinte  was  separated  from  the  first  by  a dry 
ditch,  which  favored  sorties,  and  whicli  was  provided  with 
all  the  mei|us,  as  palisades,  tambours,  and  block-houses,  for 


i 


146 


ELEMENTS  OF  PEKMANENT  /OK  IT  FICATIOX. 


offensive  returns  and  surprises.  /The  second  enceinte  was 
generally  covered  from  an  exte^r  command  by  a glacis  in 
advance  of  the  main  ditch.  Tl^  covered-way  between  the 
glacis  and  the  ditches  was,  t/  a great  extent,  deprived  of 
its  essential  offensive  feati^e  by  an  exterior  wet  ditch 
made  at  the  foot  of  the  glads  and  enclosing  it,  over  which 
communication  with  the  /xterior  was  kept  open  by  tem- 
porary bridges.  / 

The  works  were  usually  very  much  multiplied  and  their 
combination  complicatoa ; features  the  less  objectionable 
where  their  defence  chiefly  rested  upon  the  inhabitants  who 
had  become  familiar  ^ith  all  their  turnings,  and  as  offering 
obscurity  of  design  fo  an  assailant  who  might  force  his  way 
into  them.  The  w^ble  of  the  defensive  measures  of  this 
school  seem  to  haye  had  solely  for  their  object  a strictly 
passive  resistance.;  With  this  view  long  lines  of  intrench- 
ments,  supported, from  distance  to  distance  by  forts, connected 
their  frontier  to%ns  and  villages,  affording  a sufficient  ob- 
stacle to  marauding  expeditions,  and  requiring  the  efforts 
of  a strong  foyce  to  break  through  them.  At  a later  pe- 
riod, taught  by  the  experience  of  their  earlier  efforts  against 
the  most  military  state  of  that  epoch,  covers  that  would 
afford  security  against  incendiary  modes  of  attack  were 
provided  ; a,nd  revetments  of  masonry  substituted  for  the 
earthen  slopes  of  the  ramparts,  particularly  wdiere  the 
ditches  were  dry.  These  successive  changes,  partly  influ- 
enced by  the  Italian  and  Spanish  schools,  with  which  the 
Dutch  engineers  were  brought  into  contact  through  their 
connection  with  Spain,  were  the  natural  precursors  of  the 
system  of  Coehoorn,  the  most  distinguished  engineer  of  the 
Dutch  school,  whose  works  are  characterized  by  many  of 
its  essetitial  features. 

287.  German  School.  The  Germans  reckon  a number 
of  original  writers  on  fortiflcation,  among  the  most  noted 
of  whom  are  the  celebrated  painter,  Albert  Durer,  Daniel 
Speckles,  and  Kimpler.  In  the  propositions  of  these  writers 
are  to  be  found  the  influence  which  the  Italian  school  natu- 
rally'exercised  throughout  civilized  Europe,  and  the  germs 
of  many  of  the  views  held  by  the  German  school  of  the 
present  day  ; wdiich  last  seem,  however,  to  have  been  taken 
more  immediately  from  the  propositions  of  Montalembert 
and  Carnot. 

288.  Swedish  School.  The  part  played  by  Sweden 
upon  the  theatre  of  Europe,  under  her  two  celebrated  mon- 
archs,  Gustavus  Adolphus  and  Charles  XII.,  served  to  de- 


ELEMENTS  OF  PERMANENT  FORTIFICATION.  14? 

y 

Nelop  in  this  nation  every  branch  of  th^  military  art,  and 
produced  a number  of  distinguished  genferals  and  engineers, 
who  combined  with  the  practice  of  th^r  profession  a study 
of  its  theory.  Among  the  engineers /f  this  school,  Virgin 
holds  the  first  place.  / 

The  climate  and  the  nautical  habrfs  of  the  country  seem 
to  have  led  to  land  defences  analo^us  to  those  of  ships,  as 
shown  in  the  uses  of  casemated  fatteries  in  several  tiers, 
both  for  sea-coast  and  inland  fortmcations.  In  this  school 
the  bastioned  system  seems  to  h^e  been  generally  adopted 
for  the  enceinte,  great  attention  peing  paid  to  covering  the 
faces  of  the  works  from  enfilading  fire ; in  providing  case- 
mates having  reverse  views  on|  the  besiegers’  works ; and 
particularly  in  so  arranging  tie  interior  dispositions  that 
each  part  should  not  only  con^ibute  to  the  defence  of  the 
others,  but  be  capable  of  an  independent  resistance.  These 
dispositions  necessarily  led  tdgreat  complication  and  mul- 
tiplicity of  works,  as  shown  ii  the  writings  of  Virgin. 

289.  French  School.  What  may  be  termed  the  charac- 
teristics of  this  school  are  to|be  seen  rather  in  the  method 
of  Cormontaigne,  and  the  tfachings  of  the  two  celebrated 
schools  of  Mezieres  and  Met|  for  the  education  of  engineers, 
than  in  the  practice  of  Vaulan,  although  his  authority  has 
exercised  a preponderating!  infiuence  throughout  Europe, 
and  is  still  appealed  to,  in  ^1  great  problems  of  the  art,  by 
each  side  in  polemical  disputes. 

The  French  have  evince^  in  this,  as  in  all  the  other  arts, 
that  spirit  of  systematic  combination  which  forms  one  of 
their  most  striking  national  traits.  Without  excluding  an 
active  defence,  the  most  noted  authors  of  this  school  have 
based  their  methods  upomja  combination  of  elements  by 
which  the  besieger’s  progre^  can  be  checked  step  by  step  by 
the  fire  of  the  works  rathdr  than  by  sorties.  Within  the 
last  twenty  years  all  school!  have  been  rapidly  tending  tow- 
ards a common  system,  wh|ch  is  the  logical  outcome  of  the 
weapons  now  available,  aifd  the  means  of  resisting  their 
action.  ^ 

The  freedom  of  intercoiAse  between  nations,  no  less  than 
the  general  and  free  discussion  of  all  projects  by  all  en- 
gineers, leads  to  the  develoj^ment  and  adoption  of  the  sim- 
plest, cheapest,  and  most  effective  methods  of  defence. 
That  a universal  system  is  yet  adopted  can  hardly  be  said, 
but  the  disposition  to  depend  mainly  upon  a defence  by  de- 
tached works,  as  previously,  described,  is  too  manifest  to 
leave  room  for  a reasonable  dopbt  that  for  many  years  it  will 
be  the  only  one  employed. 


(.48 


ELEMExSllS  OF  PEKMANEifT  FORTIEICATIOI^. 


II. 


PROGBESS  OF  THE  ATTACK  SINCE  THE  INVENTION  OF  FIRE* 

ARMS. 

290.  The  introduction  of  cannon,  although  it  led  to  ira- 
portant  changes  in  the  measures  both  of  the  attack  and  de- 
fence, still  did  not,  for  a considerable  period,  bring  about 
any  very  decisive  results  in  the  length  of  sieges.  The 
means  which  it  afforded  the  defence  of  reaching  the  besieg- 
ers  at  a distance,  and  of  destroying  all  the  methods  of  ap- 
proaching and  annoying  the  place  which  had  been  hitherto 
used,  led  to  the  substitution  of  the  ordinary  trenches  of  the 
present  day  for  the  wooden  galleries  and  other  similar  ex- 
pedients for  approaching  under  cover,  and  to  the  erection  of 
batteries  at  distant  points  to  open  breaches  in  the  walls. 

Lines  of  circumvallation  and  countervallation,  which 
formed  so  prominent  a feature  previously  to  this  epoch,  was 
the  only  one  which  still  kept  its  place,  as  it  has  done  to  a 
greater  or  less  extent  to  the  present  day.  For  the  purpose 
of  effecting  an  entrance  into  the  place,  breaching  batteries 
were  erected  opposite  the  points  deemed  most  favorable. 
They  were  placed  either  on  natural  elevations  of  the  ground, 
or  upon  artificial  mounds,  with  the  object  of  striking  tlie 
wall  to  be  opened  near  its  foot,  and  forming  a breach  of  easy 
ascent.  These  batteries  were  enclosed  in  works  of  sufficient 
size  and  strength  to  hold  garrisons  to  secure  them  from 
sorties.  The  approaches  were  made  as  at  present,  by  zig* 
zags  along  the  capitals  of  the  salients  to  the  counterscarp, 
where  a covered  descent  was  made  into  the  ditch  opposite 
the  breach  preparatory  to  its  assault.  When  the  wall  was 
not  exposed  to  a distant  fire,  the  besiegers  were  obliged  to 
carry  the  covered- way  by  assaidt,  and  establish  their  breach- 
ing batteries  on  the  crest  of  the  glacis. 

In  carrying  forward  these  works  the  besiegers  were  sub- 
jected to  great  losses  and  delays,  owing  to  the  magnitude 
and  multiplicity  of  the  works  they  were  obliged  to  com- 
plete, to  the  imperfect  character  of  their  artillery  and  the 
faulty  position  of  their  batteries,  by  vdiich  they  were  unable 
to  keep  under  the  fire  of  the  place ; the  want  of  connection 
between  the  separate  approaches,  and  the  consequent  ex- 
posure of  the  workmen  in  the  trenches  to  sorties,  the  troops 
for  their  support  being  too  distant  in  the  enclosed  works  in 
the  rear  to  give  them  timely  succor;  besides  which,  as  these 


ELExMENTS  OF  PERMANENT  FORTIFICATION. 


149 


enclosed  works  naturally  became  the  chief  objects  for  the 
tire  of  the  besieged,  this  agglomeration  of  troops  in  them 
added  materially  to  the  losses  of  the  besiegers. 

Owing  to  these  imperfections  in  the  measures  of  attack, 
the  besieged  were  able  to  make  a vigorous  and  prolonged 
defence  ; and  sieges  became  the  most  important  military 
operations  of  this  period,  in  which  captains  of  the  greatest 
celebrity  sought  for  opportunities  of  distinction. 

291.  But  little  deviation  was  made  in  the  methods  just 
described  until  Yauban  appeared  upon  the  scene.  Pre- 
vious to  him,  Montluc,  a distinguished  French  general  and 
engineer,  had  introduced  short  branches  of  trenches,  which 
were  run  out  from  the  angles  of  the  zigzags,  to  post  a few 
troops  for  the  immediate  protection  of  the  workmen  ; but 
these  were  found  to  be  very  insufficient  in  repelling  sorties 
of  any  strength. 

The  event  which  seems  to  have  had  the  greatest  influence 
on  the  subsequent  progress  of  both  the  attack  and  defence 
was  the  memorable  siege  of  Candia,  in  which  volunteers 
from  all  parts  of  Europe  engaged,  who,  after  its  close, 
disseminated  throughout  their  respective  countries  the  re- 
sults of  the  experience  they  had  there  acquired. 

Whether  the  idea  of  the  parallels,  now  in  use  in  the 
attack,  originated  there,  or  with  Yauban,  this  eminent  jnan 
was  the  first  to  establish  them  in  a systematic  manner,  and 
to  demonstrate  by  experience  their  controlling  importance 
in  repressing  sorties.  The  introduction  of  this  important 
elcTnent  in  the  attack ; the  concentration  of  the  fire  of  bat- 
teries, by  giving  them  enfilading  positions ; the  invention 
of  the  ricochet,  as  the  most  powerful  destructive  means 
against  the  defences ; the  avoidance  of  open  assaults,  which, 
even  when  successful,  are  made  at  a great  sacrifice  of  life, 
preferring  to  them  the  less  brilliant  but  slower  method  of 
skill  and  industry,  by  which  the  blood  of  the  soldier  is 
spared,  and  the  end  more  surely  attained, — such  are  the  im- 
portant services  which  the  attack  owes  to  Yauban,  which 
gave  it  its  marked  superiority  over  the  means  of  defence. 

From  the  preceding  brief  summary,  it  will  be  seen  that 
the  art  of  fortification,  in  its  progress,  has  kept  pace  with 
the  measures  of  the  attack;  its  successive  changes  having 
been  brought  about  by  changes  either  in  the  arms  used  by 
the  assailant,  or  by  the  introduction  of  some  new  mode  of 
assault.  The  same  causes  must  continue  to  produce  the 
same  effects.  At  no  past  period  has  mechanical  invention, 
in  its  bearing  on  the  military  art,  been  more  active  than  at 


150 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


the  present  day.  The  improvement  that  has  been  made  in 
tlie  range  and  accuracy  of  aim  of  both  small-arms  and  can- 
non, the  adoption  of  wrought  iron  and  steel  for  floating 
batteries  and  sea-coast  defences,  form  the  commencement 
of  another  epoch  in  the  engineer’s  art.  The  great  im- 
provements in  cannon  give  to  the  assailant  a still  wider 
range  in  the  selection  of  positions  for  his  batteries,  and  thus 
increase  the  difficulties  of  the  engineer  in  adapting  his 
works  to  the  site,  and  in  giving  adequate  shelter  to  the  gar- 
rison and  armament.  AVhilst  the  defence  is  to  this  extent 
weakened,  the  approaches  of  the  besieger  are  rendered  more 
perilous  and  more  difficult  from  the  greater  range  and 
accuracy  of  small -arms. 

The  great  destruction  of  life  in  open  assaults  by  columns, 
exposed  within  so  long  a range,  gives  an  additional  value  to 
intrenched  flelds  of  battle  ; and  we  will  again  see  field- 
works play  the  part  they  did  in  the  defence  of  Sebastopol 
and  Plevna,  and  positions  so  chosen  and  fortified  that  not 
only  will  the  assailant  be  forced  to  intrench  himself  to  assail 
them,  but  will  And  the  varying  phases  of  his  attack  met  by 
corresponding  changes  in  the  defensive  dispositions. 

292.  In  our  own  country,  from  the  circumstances  of  our 
position,  permanent  fortification  has  met  with  its  most  fre- 
quent applications  in  works  planned  for  sea-coast  defence, 
in  which  our  engineers,  without  servilely  copying  any  of 
the  systems  in  vogue  in  Europe,  have  followed  the  bas- 
tioned  system,  wherever  the  works  were  of  such  an  extent 
as  to  admit  of  its  application. 

In  the  larger  works  erected  by  them  for  sea-coast  defence, 
the  water  fronts  consist  of  one  or  more  tiers  of  casemated 
batteries,  surmounted  by  one  in  barbette,  whilst  the  land 
fronts  consist  of  the  usual  rampart  and  parapet  arranged  for 
open  defences. 

In  the  smaller  works,  which,  from  the  limited  extent  of 
their  fronts,  did  not  admit  of  the  adoption  of  the  bastiont'd 
system,  flanking  dispositions  have  been  made,  either  by 
casemated  caponnieres  or  counterscarp  galleries. 

Wherever  the  site  was  very  limited,  and  a large  amount 
of  Are  in  a given  direction  was  desirable,  as  in  the  cases  of 
islands  (either  natural  or  artificial)  to  be  occupied  on  the  line 
of  a channel  to  a roadstead  or  harbor,  the  castellated  form, 
consisting  of  several  tiers  of  casemates,  surmounted  by  a 
barbette  battery,  has  been  adopted.  These  works  are  gen- 
erally so  surrounded  by  water  as  to  be  secure  from  an  open 
assault,  and  therefore  not  requiring  flanking  dispositions. 


ELEMENTS  OF  PEEMANENT  FORTIFICATION. 


151 


Where,  however,  it  has  been  thought  necessary  to  place 
these,  small  bastioned  towers  have  been  added  at  the  salient 
auijles  of  the  work. 

Whilst  thus  adhering  to  well-settled  principles,  and  fol- 
lowing the  practice  of  the  best  European  authorities,  our 
engineers  have  contributed  their  share  to  the  improvement 
of  the  details  of  the  art.  The  works  erected  by  them  are  * 
remarkable  for  the  excellence  of  the  materials  employed,  the 
great  skill  shown  in  their  construction,  and  the  care  with 
which  every  detail  was  worked  out  to  subserve  the  object  in 
view.  In  these  respects,  in  the  inventive  genius  often  dis- 
played, and  in  the  adaptation  of  the  plan  to  the  site,  it  is 
not  claiming  too  much  to  say  that  the  works  erected  by 
them  are  not  surpassed,  and  in  some  points  not  equalled,  by 
any  similar  works  in  Europe. 

Our  engineers  have  for  many  years  reported  that  these 
works  are  now  entirely  inadequate  for  the  defence  of  our 
harbors,  and  have  urgently  advocated  that  they  be  replaced 
at  once  by  those  which  can  resist  modern  guns  as  well  as 
afford  emplacements  for  them. 

A popular  interest  in  this  subject  seems  at  last  to  have 
been  awakened,  and  it  is  to  be  hoped  that  measures  will  soon 
be  taken  to  provide  our  harbors  and  exposed  cities  with  a 
suitable  defence,  by  supplying  them  with  fortifications  and 
guns. 

293.  The  further  changes  that  will  be  required  in  fortifi- 
cations both  for  attack  and  defence,  so  far  as  indicated  by 
the  progressive  improvements  in  arms,  the  increased  use  of 
mortars  and  the  proposed  employment  of  dynamite  and 
other  high  explosives  in  shells,  will  consist  princip'allyin 
giving  greater  strength  to  parapets  and  armor,  extending 
still  further  the  use  of  armored  constructions  and  bomb- 
proof covers,  giving  them  greater  thickness,  and  in  so  con- 
structing splinter  proofs  that  they  will  give  protection  from 
splinters  whose  velocity,  arising  from  a high  explosive,  will 
not  only  give  them  greater  penetration,  but,  by  exceeding 
that  of  the  shell  from  which  they  come,  will  take  the  para- 
pets and  shelters  in  reverse. 

None  of  these  involve  changes  in  principle  nor  great 
changes  in  detail,  and  it  is  probable  that  fortifications  built 
in  accordance  with  methods  now  adopted  and  approved  will 
for  many  years  fulfil  all  the  requirements' of  an  efficient  de- 
fence. 


152 


ELEMEisTS  OE  PEEMAi^Ei^T  EUKTIPlCJATiuX. 


CHAPTER  XII. 

MODERN  CONSTRUCTIONS  IN  IRON  AND  STEEL. 

294.  Iron  armor,  although  advocated  bj  Gen.  Paixhan, 
and  Robert  Stevens,  of  Hoboken,  X.  J.,  so  early  as  1841-42, 
received  its  first  test  in  actual  conflict  in  the  attack  of  the 
French  and  English  iron-clad  batteries  on  the  Kinburn 
forts  in  the  Crimean  war  in  1855. 

The  results  of  this  attack  led  to  its  further  application,  in 
both  France  and  England,  for  naval  purposes;  but  a new 
and  marked  impulse  was  given  by  the  startling  results  ob- 
tained by  its  use  in  the  civil  war  of  1861-65, 

295.  In  the  development  of  armor,  wrought-iron  natu- 
rally took  the  lead,  although  experimental  constructions  in 
steel  were  made  so  early  as  1857,  and  in  compound  plates  in 
1859. 

In  its  earlier  application,  both  singly  and  in  combination 
with  iron,  steel  was  found  brittle  and  easily  broken  up  by 
the  projectiles. 

It  was  not,  however,  abandoned,  but  continued  experi- 
ments were  made  by  English  and  French  manufacturers, 
who  produced  the  first  successful  compound  plate  in  1867, 
and  steel  plate  in  1876. 

Meanwhile  the  manufacturers  had  improved  the  quality 
and  increased  the  thickness  of  iron  plates,  producing  them 
of  guaranteed  quality  12  inches  thick,  and  of  good  quality 
up  to  22  inches  thick  which  were  tested  in  competition  with 
steel  plates  of  22  inches  in  the  last-named  year. 

Competitive  trials  of  compound  plates  and  those  made  of 
steel,  each  18.9  inches  thick,  were  also  carried  on  in  1882, 
the  results  of  both  trials  being  rather  in  favor  of  the  steel 
plates. 

Although  some  of  these  proved  quite  brittle,  constant 
improvement  was  made  in  the  manufacture  of  both  com- 
pound auQ  steel  plates ; the  introduction  of  a small  per 
cent  of  nicEel  in  the  latter  by  Schneider  et  Cie  of  Creusot 
marking  a ve.  y material  advance. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


153 


In  the  United  States,  the  recent  development  of  nickel- 
rsteel  armor  witli  the  face  hardened  by  the  Harvey  process 
has  resulted  (1892 j in  the  production  of  plates  which  com- 
bine toughness  and  hardness  to  an  extent  hitherto  unknown, 
and  which  have  a resisting  power  far  greater  than  any 
others  made. 

Chilled  cast-iron  was  first  introducea  by  Grfison,  in  Ger- 
many, in  1868,  and  has  been  gaining  ground  for  land  de- 
fence since  that  time,  its  great  weight  precluding  its  use  on 
vessels. 

296.  Under  the  impact  of  projectiles,  wrought-iron,  by 
means  of  its  ductility  and  relative  lack  of  tenacity,  is  pene- 
trated by  the  projectile  in  a manner  similar  to  that  of  a 
plate  of  lead  by  a punch.  The  injury  is,  with  the  best 
plates,  almost  entirely  local,  and  if  the  plate  be  not  pierced 
it  has  nearly  as  much  resisting  power  as  before,  in  points  a 
little  removed  from  that  struck. 

In  the  immediate  vicinity  of  a previous  blow  the  resist- 
ance is  diminished,  because  the  metal  fiows  laterally  into  the 
liole  produced  by  the  preceding  shot. 

When  the  blows  are  of  great  energy,  and  the  plate  is  not 
large,  or  is  of  poor  quality,  it  is  generally  destroyed  by  crack- 
ing and  breaking. 

The  best  steel  projectiles  are  not  materially  deformed 
even  by  the  thickest  iron  plates,  their  energy  being  ex- 
pended upon  the  plate  and  not  upon  themselves.  Their 
penetration  can  be  quite  closely  calculated. 

297.  Compound  armor  behaves  quite  differently.  Its 
hard  steel  face  is  either  very  slightly  penetrated,  and  shows 
hut  little  injury  from  the  shot,  or  radial  and  concentric 
cracks  of  greater  or  less  depth  are  produced  about  the  point 
of  impact,  and  the  projectile  gets  through  the  armor  more 
by  a process  of  breaking  up  and  displacing,  than  by  pene- 
trating it. 

The  best  steel  projectiles  are  frequently  broken  up  by  the 
plates. 

298.  Steel  plates  with  a less  per  cent  of  carbon  than 
the  face  of  the  compound  plates,  behave  in  a manner  inter- 
mediate between  wrought-iron  and  compound  plates.  They 
are  penetrated  more  deeply  than  the  compound  but  less  than 
the  iron  plates,  while  they  crack  more  readily  than  the  iron, 
and  perhaps  less  so  than  the  compound.  The  cracks  are 
.almost  exclusively  radial. 

The  projectiles  may  pierce,  but  more  frequently  destroy 


io-i  ELEMENTS  OF  PERMANENT  FORTIFICATION. 

the  plate  by  breaking  it  up.  Steel  projectiles  are  usually 
broken  up,  but  occasionally  rebound  after  striking,  or  pass 
through  unbroken. 

299.  Chilled  iron  has  an  extremely  hard  surface.  No 
projectile  has  yet  been  made  which  produces  a deep  pene- 
tration or  which  has  not  been  broken  into  pieces  when  fired 
against  it.  It  can  hardly  be  called  penetrable.  Under  re- 
peated blows  it  is  split  into  blocks,  along  the  planes  of  weak- 
ness arising  from  crystallization,  which,  by  their  wedge  shape,, 
frequently  resist  a number  of  blows  without  displacement. 

Its  protective  value  is  destroyed  by  the  displacement  of 
the  broken  parts  or  by  the  bodily  movement  of  the  shield 
under  the  blows  of  the  projectiles. 

Being  a cast  metal,  the  shields  are  easily  made  of  any 
thickness  required,  with  surfaces  of  double  curvature  of 
any  desired  convexity. 

300.  In  designing  armor  for  land  defences,  engineers  are 
not  hampered  by  many  considerations  wdiich  attach  to  iron- 
clad ships.  On  land  the  weight  of  armor,  as  previously 
stated,  is  sometimes  an  advantage.  This  allows  the  use  of 
chilled  iron  or  wrought  iron  of  any  desired  thickness.  The 
necessity  for  covering  a definite  height  with  armor  is 
obviated  by  the  use  of  impenetrable  substructures  of  masonry 
and  earth. 

This  permits  the  application  of  spheroidal  and  dome-shaped 
structures  which  only  admit  of  oblique  impacts  and  present 
the  smallest  and  most  indistinct  targets  to  the  enemy. 

The  domes  recently  introduced  by  the  Germans  (Schu-= 
mann’s  design,  Griison’s  make,)  will  probably  be  largely 
used.  They  are  made  in  the  shape  of  spherical  segments  of 
such  slight  convexity  that  they  admit  of  the  use  of  wrought 
iron,  steel,  or  compound  metal. 

301.  In  the  armored  forts  constructed  by  England  since 
1860,  as  previously  stated,  iron  shields  are  in  some  cases 
used  to  cover  the  gun  chambers  in  granite  structures,  of 
several  tiers  of  fire.  These  shields  are  of  wrought  iron, 
usually  consisting  of  three  plates  each  about  5 inches  thick 
separated  by  concrete,  the  embrasures  being  fitted  for  the 
old  type  of  carriages. 

In  the  large  forts  on  Horse  Shoal  and  No  Man’s  Land  at 
Portsmouth,  circular  in  form  and  to  mount  49  guns  in  two 
tiers,  the  exterior  superstructure  is  entirely  of  iron,  the 
front  being  of  a construction  about  the  same  as  the  shields, 
above  described. 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


I55 


302.  The  English  engineers  have  also  used  wrought  iron 
turrets  in  their  sea-coast  works ; the  cylindrical  type  being^ 
selected,  probably  because,  at  the  time  they  were  built,  their 
armor-makers  had  such  large  experience  and  skill  in  build- 
ing turrets  of  this  shape,  and  from  the  simplicity  of  their 
construction.  They  are  still  preferred  by  some  engineers. 

303.  Plate  18,  Fig.  7,  is  a vertical  section  of  the  turret 
at  the  outer  end  of  the  pier  at  Dover.  Its  interior  diameter 
is  32  feet,  height  of  armor,  9 feet;  thickness  of  armor, 
25  inches,  in  three  plates  of  7 inches  and  two  of  2 inches. 
The  roof,  2 inches  thick,  is  only  splinter  proof,  is  partly 
grating,  and  the  parts  directly  over  the  guns  are  removable 
to  allow  the  guns  to  be  taken  out  or  replaced.  The  weight 
of  the  turret,  without  guns,  is  460  tons.  The  total  weight  of 
turret,  mounting,  guns,  and  carriages,  is  about  895  tons. 

304.  The  turret  itself  is  carried  on  a framed  support  of 
steel  turning  on  a central  pivot  and  carried  by  32  rollers 
running  on  a track  placed  on  a masonry  substructure. 

The  central  pivot  is  built  up  of  wrought  iron,  and  is  very 
strong.  It  is  enclosed  in  a cylinder  of  Bessemer  steel,  and 
outside  this  is  a heavy  casting  firmly  fastened  to  the  masonry. 
The  turret  is  turned  by  a pinion  and  toothed  wheel  driven 
by  steam-power. 

The  engines  and  magazines  are  about  30  feet  below  the  level 
of  the  guns,  and  the  shell-rooms  in  the  intermediate  story. 

The  turret  is  armed  with  two  80-ton  muzzle-loading  guns, 
which  are  capable  of  7°  elevation  and  2°  depression.  They 
are  drawn  back  into  the  turret,  and  depressed  so  as  to  be 
loaded  from  under  the  glacis.  The  glacis  is  of  stone  ma- 
sonry covered  with  concrete,  finished  on  the  inside  with  a 
ring  of  plates  5 inches  and  3 inches  thick,  resting  on  a circle 
of  2-inch  plates. 

305.  Plate  18,  Fig.  2,  is  a section  and  interior  elevation 
of  an  experimental  turret  for  land  defences  of  French  con- 
struction (Mougin,  designer ; St.  diamond  manufacture.) 
Its  exterior  diameter  is  15f  feet;  height  of  armor,  4 feet; 
thickness,  17.7  inches  single  plate ; three  plates  make  up  the 
cylinder. 

The  top  is  of  flat  plates,  in  two  parts,  7 inches  thick, 
rabbeted  and  screwed  into  the  vertical  plates.  The  turret 
itself  rests  upon  a structure  of  plates  supported  in  the  centre 
by  a pivot,  which  serves  as  the  plunger  of  a hydraulic 
press,  by  which  the  turret  and  its  armament  may  be  raised 
for  turning,  and  lowered  before  firing.  Around  the  exterior 
are  10  rollers  whose  axes  are  horizontal,  running  on  a circu- 


156 


ELEMENTS  OF  PERMANEjnT  FORTIFICATION. 


lar  track,  and  6 with  vertical  axes  which  press  against  a 
vertical  ring. 

These  rollers  do  not  carry  the  w^eight  of  the  turret,  but 
serve  only  to  balance  and  direct  it,  and  to  relieve  the  pivot 
from  shocks.  The  pivot  is  inches  thick. 

The  hydraulic  pressure  is  obtained  by  a pump  worked  by 
hand.  It  enables  the  turret  to  be  raised  through  considerable 
distance  to  free  it  if  jammed  by  splinters,  and  allows  it  to  be 
turned  with  very  little  friction.  The  turning  is  done  by  a 
winch,  worked  by  four  men,  which  turns  a pinion  engaging 
with  a toothed  wheel  attached  to  the  turret  platform. 

The  substructure  is  of  two  stories,  the  lower  being  used 
as  a magazine,  and  for  the  rotating  and  hydraulic  machinery  ; 
the  second,  for  working  the  guns  and  serving  the  ammu- 
nition. The  guns,  with  their  attachments,  occupy  the  turret 
itself. 

The  turret  is  armed  with  two  15.5  c.m.  (6"')  De  Bange 
guns,  with  minimum  embrasure  carriages,  admitting  of  an 
elevation  of  20°  and  a depression  of  5°.  They  allow  a very 
small  recoil.  The  gun  and  carriage  are  balanced  by  a 
counterweight. 

306.  In  pointing,  the  guns  are  given  the  proper  elevation 
by  an  arc  attached  to  the  slides  in  the  usual  manner.  For 
horizontal  direction,  a graduated  arc  is  placed  under  the 
turret,  provided  with  a movable  index  for  each  gun  ; these 
are  clamped  on  the  arc  at  points  corresponding  to  the 
azimuth  of  the  object  aimed  at,  the  sighting  being  done 
through  the  bore  of  the  gun. 

Electric  contact  points  are  attached  to  the  turret  so  as  to 
touch  these  indices  when  the  guns  have  the  correct  direc- 
tion, and  firing  takes  place  automatically  when  the  turret  is 
turned  in  the  right  direction  up  to  these  contacts. 

The  glacis  armor  is  made  up  of  four  pieces  of  chilled 
cast-i]*on,  and  is  covered  with  concrete  and  sand  in  front. 

The  weight  of  the  armor  is  about  73  tons,  and  that  of  the 
glacis  about  68  tons  ; total,  141  tons. 

The  weight  of  each  gun  is  about  6400  pounds  and  each 
carriage  about  7500  pounds.  Twenty -nine  officers  and  men 
are  considered  necessary  to  work  the  turret  and  guns. 

307.  Plate  18,  Fig.  1,  shows  a vertical  section  and  in- 
terior elevation  of  an  experimental  turret  of  German  manu- 
facture (Schumann’s  design,  Griison’s  make). 

The  top  is  a spherical  segment  of  19^  feet  greatest  diam- 
eter, 17  feet  radius,  and  3 feet  rise. 

The  armor,  8 inches  thick,  consists  of  six  arched  sectors 


ELEMENTS  OF  FERMANENT  FORTIFICATION. 


15? 


and  a six-sided  central  plate.  The  plates  are  dowelled  to- 
gether and  screwed  to  a skin  of  two  plates  each,  al)out  J inch 
thick,  riveted  together. 

The  embrasure  plate,  the  two  next  it,  and  the  top  plate 
are  of  wrought  iron ; the  other  three  of  compound  armor. 

The  turret  is  supported  on  a construction  of  plate  iron, 
carried  bj  a central  pivot,  and  is  provided  with  four  rollers 
with  elastic  bearings,  under  the  periphery  at  90°  apart. 

These  rollers  run  on  a circular  track  attached  to  the 
glacis. 

The  pivot  is  about  7 inches  in  diameter,  and  rests  at  the 
bottom  on  a screw  which  is  supported  by  a wooden  block 
for  elasticity.  By  the  screw  the  turret  may  be  raised  or 
lowered  to  relieve  the  rollers  from  a part  of  the  weight. 

The  substructure  and  the  cupola  are  arranged  in  a single 
story.  Kecesses  in  the  side  walls  serve  for  storing  ammu- 
nition. 

The  glacis  armor  consists  of  eight  chilled-iron  plates. 
Their  thickness  at  top  is  14  inches,  at  bottom  8^  inches. 

They  are  covered  on  the  outside  with  concrete. 

The  turret  is  turned  with  a winch  worked  by  4 to  6 men. 

It  is  armed  with  two  25  cal.  15  c.m.  (Q")  Krupp  guns 
mounted  on  non-recoil  carriages.  The  chase  of  the  gun  in 
the  embrasure  is  supported  by  a trunnion  ring,  the  trun- 
nions resting  in  beds  in  the  armor  plates  about  which  the 
gun  turns  for  elevation  and  depression,  which  are  25°  and  5° 
respectively.  Horizontal  direction  is  given  in  the  usual  way 
by  revolving  the  turret. 

308.  The  pointing  is  done  by  thrusting  the  head  through 
a hole  in  the  roof,  the  sights  being  fitted  to  the  top ; or  by 
sighting  through  a hole  in  the  back  of  the  turret,  and  then 
revolving  it  180°  ; a graduated  circle  and  pointer  pro- 
viding for  this,  as  well  as  for  pointing  in  a fixed  direction 
without  sighting  after  the  direction  is  once  established. 

The  elevation  is  given  in  the  usual  way  by  an  arc  and 
pointer. 

The  embrasures  are  made  horizontal.  The  guns  and  car- 
riages are  counterpoised  by  a heavy  weight.  The  recoil  is 
taken  up  by  arcs  attached  to  the  turret. 

The  weight  of  the  armor  plates  is  about  46  tons,  that  of 
the  glacis  about  65  tons  ; total.  111  tons. 

It  is  stated  that  the  guns  and  turret  may  be  worked  by 
14  officers  and  men.  Griison’s  price  for  a turret  of  this  type 
is  about  $45,000. 

309.  This  and  the  French  turret  previously  described, 


158 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


were  subjected  to  competitive  trial  at  Bucharest,  in  De- 
cember, 1885,  and  January,  1886.  Figs.  3,  4,  5 and  6,  taken 
from  photographs,  show  their  appearance  after  the  trial, 
during  which  neither  turret  was  penetrated  or  disahled. 

Fig.  4 shows  the  back  of  the  French  turret  after  95  shots 
and  66  hits  with  the  15  c.m.  gun  at  1100  yards  range. 
Striking  energy  1146  foot  tons.  Fig.  6 shows  its  embrasure 
after  4 shots  at  55  yards  range  with  same  striking  energy. 

Fig.  3 shows  the  back  of  the  German  turret  after  135 
shots  and  Yl  hits  ; and  Fig.  5,  the  front,  after  7 hits  with  the 
same  ranges  and  guns. 

They  illustrate  the  behavior  of  wrought  iron  under  direct 
and  oblique  impact  and  that  of  compound  plates  under 
oblique  only. 

310.  Plate  19,  Fig.  1,  is  a plan  vertical  section  and  in- 
terior elevation  of  a revolving  turret  caponniere  for  machine 
guns  for  use  at  salient  and  shoulder  angles. 

It  consists  of  a vaulted  roof  of  wrought  iron  and  a front 
ring  of  chilled  iron,  pierced  for  two  revolving  machine  guns, 
with  a chilled-iron  glacis  covered  wdth  masonry.  The  thick- 
ness of  the  armor  is  determined  by  the  character  of  fire  to 
which  it  may  be  exposed  : the  roof  being  made  bomb-proof, 
and  both  roof  and  front  proof  against  the  oblique  blows  to 
which  only  they  are  subject.  The  dimensions  will  vary 
with  the  position  and  armament.  A thickness  of  roof  of  4 
inches  steel  or  5^  inches  wrought-iron  is  considered  suffi- 
cient for  very  small  turrets.  This  turret  is  7 feet  interior 
diameter  without  central  pivot.  It  is  supported  on  a system 
of  rollers  and  is  turned  either  by  a pinion  and  toothed  wheel 
or  by  a lever.  Entrance  to  it  is  obtained  through  a postern 
under  the  parapet,  as  shown.  The  size  here  represented, 
weighs  about  18  tons,  and  costs  at  the  manufactory  about 
$6500. 

The  details  and  dimensions  may  be  determined  from  the 
figure. 

311.  Fig.  2 is  a half  plan,  half  horizontal,  and  a vertical 
section  with  interior  elevation  of  a fixed  turret  caponniffi’e 
for  use  at  salient  angles.  It  is  somewhat  larger  than  the 
revolving  turret.  ' It  is  pierced  for  two  machine  guns  on 
each  side,  with  intermediate  loopholes  for  musketry. 

The  chilled-iron  armor  in  the  vicinity  of  the  machine 
guns  which  look  dowm  the  ditches  is  made  thicker  than  on 
the  side  toward  the  salient,  being  exposed  to  more  direct 
fire.  Entrance  to  the  caponniere  is  by  a postern,  as  in  the 
other  case.  The  machine  guns  have  sufficient  horizontal 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


159 


traverse  to  sweep  the  whole  width  of  the  ditch,  and  an 
elevation  and  depression  of  about  15°  and  5°  respectively. 

312.  Figs.  3 and  4,  are  sections  and  interior  elevations  of 
a disappearing  turret  for  a 37  mm.  (1".45)  machine  gun. 

In  this  construction  the  roof  is  made  bomb-proof,  varying 
as  previously  stated  (art.  310)  from  4 inches  in  steel  to  5| 
inches  in  iron-.  The  vertical  wall  through  which  the  gun 
fires  is  of  steel  and  varies  in  thickness  from  ^ inch  to  3 
inches  in  different  constructions,  depending  upon  the  fire  to 
which  it  is  exposed. 

The  turret  gun  and  carriage  are  supported  on  a framed 
structure  carried  by  a central  pivot  which  terminates  in  a 
rounded  end. 

The  end  of  the  pivot  rests  upon  and  turns  in  a bearing 
which  is  carried  by  a stirrup  sliding  vertically  in  a slot  in  a 
hollow  cylinder,  outside  of  which  is  a counterweight.  The 
counterweight  and  stirrup  are  connected  by  chains  passing 
over  pulleys. 

Attached  to  the  bottom  of  the  stirrup  and  passing  down 
through  the  axis  of  the  hollow  cylinder  is  a chain  which  is 
led  to  a windlass  in  the  postern. 

The  windlass  is  supplied  with  a crank  and  brake.  When 
the  brake  is  loosened,  the  counterweight  falls  and  raises  the 
turret  to  its  firing  position  16  inches  above  its  lowest  posi- 
tion. It  is  lowered  by  the  windlass  and  chain  which  draw 
down  the  stirrup  and  raise  the  counterweight.  When 
down,  the  bomb-proof  top  rests  on  the  glacis  plates. 

Three  conical  rollers  attached  to  the  vertical  cylinder 
serve  to  centre  the  turret  in  its  firing  position  by  bearing 
against  the  inner  edge  of  the  glacis  plates. 

The  gun  and  carriage  are  supported  on  two  levers  joined 
to  the  floor  of  the  chamber  and  the  gun-carriage  by  pin 
bearings,  so  as  to  allow  the  gun  to  be  drawn  back  within 
the  turret  as  shown  in  the  dotted  lines,  or  to  be  thrust  out 
for  firing,  in  which  position  it  is  held  by  a catch  attached 
to  the  armor.  Three  men  are  sufficient  to  work  the  gun 
and  turret. 

Accurate  aim  is  taken  by  the  motion  of  the  carriage,  an 
approximate  pointing  by  turning  the  turret. 

313.  This  turret  costs  at  the  factory  about  $4500,  and 
the  gun  about  $1250.  A similar  one  for  a 53  mm.  (2") 
gun  costs  about  $7000,  and  the  gun  about  $3500. 

314.  These  small  disappearing  turrets  are  applicable  to 
ditch  defence,  but  were  also  designed  for  use  in  the  parapet 
of  the  forts  for  sweeping  the  ground  in  front ; the  small 


160 


ELEMENTS  OF  PERMANENT  FORTIFICATION. 


calibres  for  repelling  assaults  and  general  fire  against  troops ; 
and  the  larger  for  retarding  the  besieger’s  approaches  in 
in  addition. 

Figs.  1,  2,  3,  and  4,  are  from  designs  of  Major  Schumann, 
Prussian  Engineers,  and  are  made  by  Griison. 

The  construction  of  disappearing  turrets  for  6-inch  guns 
is  now  seriously  considered  in  France.  ^ 

315.  The  frontispiece,  taken  from  a photograph,  of 
Battery  St.  Marie,  at  Antwerp,  shows  the  use  of  chilled -iron 
armor  in  casemates.  The  mortised  channel  in  the  edge  of 
the  plates  is  filled  with  zinc  solder  to  fasten  the  plate  to  its 
neignbor.  The  chill  does  not  extend  quite  to  this  channel. 
The  details  of  construction  are  shown  by  the  figure. 


APPENDIX  I, 


PENETRATION  OF  PROJECTILES  AND  THICK- 
NESS OF  PARAPETS. 

FORMULAS. 

All  formulas  have  been  reduced  to  the  form  E = in  which  E represents  the 

enersry,  in  foot-tons  per  inch  of  shot’s  circumference,  required  to  perforate  an  un- 
backed wrought-iron  plate  whose  thickness  in  inches  is  f,  and /(f.)  the  particular 
function  of  t. 


n«». 

Maj.  W.  H.  Noble, 
Royal  Artillery. 

t=J^wvi 
y nrgk 

E=  1.384f2. 

(r  = 6 inches.) 

V = velocity  on  im- 
pact in  ft.  per  sec. 
W = wt.  of  shot.  lbs. 
Sf  = accelerating 
force  of  gravity, 
r = radius  of  shot, in. 
k = constant,  de- 
pends on  kind  of 
iron  and  nature 
and  form  of  head 
of  shot. 

Maj.  W.  R.  King, 
U.  S.  Engineers. 

E — a.tX\og 
a = 39.  b = 0.1. 

E = 39.f 

X log(0.U-f  1). 

M.  Helie. 

E = 4A0t^- 

II 

o 

Maj  W.  H.  Noble, 
Royal  Artillery. 

‘ ='i/Srs- 

£7=  2.53fi-6. 

Andrew  Noble. 

II 

co|  1 
- 

ooj  1 

£7=  3.18fi-6. 

Col.  Maitland. 

t ^ 

''  “ 4.7337rr3. 

£7=  14.199f. 

(r  = 6 inches.) 

e = total  energy  on 
impact  in  ft. -tons. 

English, 

For  thick  plates. 

2 036 

y oT^' 

£7  = 0.86f2-o35. 

Italian. 

y 4.154' 

£7=  4.154fi-4, 

Gen.  Frolotf. 

W 

X = ~ V 

Cf2 

ITF2 

~ 4nrg2m' 

d = diam.  shot,  in. 

Capt.Orde  Browne, 
Royal  Artillery. 

II 

£7  = cf2. 

*c  depends  for  its 
value  on  the  ratio 
of  the  thickness  of 
the  plate  to  diam. 
of  shot. 

Col.  M.  de  Brettes. 

Zf  = .1052  -1-  1105. 

E = '^  (.0136f2+5.87f). 

Zf  = energy  in  me- 
tre kilogrammes 
per  square  cm.  of 
shot’s  cross  - sec- 
tion. 

5 = thickness  of 
plates  in  centime- 
tres. 

D = diam  of  shot  in 

n f 1 m » f c 

Adts. 

Zf  = 1.431.565  2 

-f  85.13645. 

.1939^2  \ 

2\4-4.5412f.^ 

Krupp. 

£7 

2V  .0135/ 

centimetres. 


* 0.5  .6  .7  .8  .9  1.0  1.1  1.2  1.3  1.1  1.5  1.6  1.7  1.8  1.9  2.0 

c = 1.300  1.250  1.178  1.125  1.083  1.050  1.022  1.000  0.981  0.964  0.950  0.938  0.926  0.917  0.908  0.900 

Capt.  Orde  Browne  gives  the  following  approximate  rule  for  penetration:  “The 
penetration  of  projectiles  into  wrought-iron  is  one  calibre  for  every  thousand  feet 
of  velocity.”  Very  accurate  results  are  obtained  by  its  use. 

11 


162 


APPENDIX. 


Calculated  Penetrations.* 

1 At  3500  Yards. 

•ajiuuj£> 

Feet. 

8.7 
6.6 

5.7 

7.5 

5.5 

4.5 

6.3 

5.5 
4.9 

4.3 

4.2 

3.6 

2.7 

2.2 
2.2 

'laAPJJC)  qjiAV 

paxixu  puus 

Feet. 

43.3 

32.8 

28.3 

37.5 
28.2 

22.8 

32.1 

28.5 

24.6 
22.0 

21.3 

18.3 

14.2 

11.4 
11.4 

•Auio  AA^aH 

Feet. 
73  2 

55.3 

48.1 

63.3 
47.5 

38.4 

54.1 

46.9 

41.5 

37.3 
36.0 

30.9 
23  8 

19.3 
19  3 

At  2000  Yards. 

•aqiu'B.io 

Feet. 

9.3 

7.2 

6.6 

8.1 

6.3 

5.1 

7.0 

6.1 
5.5 
5.0 
4.8 

4.2 

3.3 

2.7 

2.7 

'laA'BJO  IIJLA 

paxiui  puus 

Feet. 

46.5 

36.1 

32.8 

40.6 

31.5 

25.5 

35.2 

30.9 

27.6 

25.0 

24.1 

21.1 
16.0 

13.7 

13.8 

AAuaH 

Feet. 

78.6 

60.9 

55.5 

68.5 

53.1 

42.9 

59.5 

52.2 

46.5 

42.3 

40.6 
35.5 
28.2 

23.2 

23.4 

At  1000  Yards. 

•ajuiu.if) 

Feet. 

9.7 
7.0 

7.0 

8.5 

6.7 

5.4 

7.5 

6.6 

6.0 

5.0 
5.2 

4.6 

3.7 

3.1 
3.1 

•pAUJO  miAv 
paxiui  pans 

Feet. 

48.9 

38.4 

34.9 

42.9 

33.7 

27.4 

37.5 

33.1 
.29.7 

27.1 

26.1 
23.2 

18.7 

15  7 

15.8 

.^Auajj 

Feet. 

82.5 

64.8 

59.1 

72.3 

57.0 

46.2 

63.3 

55.8 

50.1 

45.9 

44.1 

39.1 

31.6 

26.5 

26.5 

N 

3 

<1 

•aiiu'Bjf) 

Feet. 

10.2 

8.2 

7.5 

9.0 
7.2 

5.8 

7.9 

7.0 
6.4 
5.8 
5.7 

5.1 

4.2 

3 6 
.0 

•laAuan  qipvv 
paxiui  pnug 

Feet. 

51.1 

40.9 

37.2 

45.1 

36.1 

29.4 

39.9 

35.4 

31.9 

29.4 

28.3 

25.5 
21.0 

17.8 

18.1 

•Auio  ^AuaH 

Feet. 

85.5 

69.1 

62.2 

76.2 

71.0 

49  8 

67.2 

59.8 

53.8 

49.6 

47.8 

43.0 
35.4 

30.1 
30.0 

•/£(}iooi9A 

Feet. 

1,835 

2,017 

1,695 

1,835 

1,985 

1,617 

1,857 

1,837 

1,768 

1,791 

1,726 

1,808 

1.772 

1.773 
1,827 

•JO  jqSiaAv  ‘oiiJoaCoaj 

Lbs. 

2,240 

1,632 

1,762 

1,560 

1,155 

1,155 

1,003 

760 

614 

476 

476 

310 

172 

113 

111 

•egjuqO 

JO  jqSpAi  ‘J9PAVOJ 

Lbs. 

750 

615 

462 

J 520 
1 462 

297 

357 

253 

183 

150 

150 

99 

57 

j 37.4 
139.6 

•jqSiaAi 

Tons. 

108 

119 

71 

75.3 

51.1 
48 
37 

27.2 
20.5 
18.9 

13.3 
7.0 

4.7 

Krupp’s 
B.  L.  Cannon. 

- ................ 

c - •*  - - 

01 

<o 

£3  3 33333333  3 

'5 

0 

o«  eo  ojooeoeoeoeoeoeo  so 

33  3 33.^3--. 

bo  a s a 

a a & ^5^5saaaaB  | 

1 1 ^ ts 

* The  above  computations  were  made  by  Lieut.  F.  E.  Hobbs,  Ordnance  I»epartment,  U.  S.  A.,  from  Ueueral  Froloff’s  formula. 


aotital  penetration  of  rifled  cannon  Into  earth,  granite,  concrete,  etc.* 


APPEi^DIX. 


163 


Remarks. 

Mean  of  43  shots. 

Penetration. 

o S S . f-  S . 1 ^ . 

- Qi  ^ CO 

$5  o 3b 

Velocity 

at 

Impact. 

Feet. 

1,424 

1,893 

1,497 

1,416 

1,875 

1,452 

1,452 

1,586 

1,512 

1,329 

Weight 

of 

Proj. 

lbs. 

408 

80 

100 

*408 

80 

100 

100 

1,700 

2,200 

397 

Cali- 

bre. 

in. 

10 

6 

6.6 

10 

6 

6.6 

6.6 

80  tons. 
17.7 
17.7 
9.22 
9.62 
12 
10 
9 
12 
10 
9 
12 
10 
9 

Gun. 

o P3  « « p3  « P3  .pi 

^ •••••• 

X j j J j *-3  ^ 2 j 

O.  • • ••  •••••••••• 

j>  ^ ^ 

Dis- 

tance. 

Yds. 

145 

145 

145 

195 

195 

195 

195 

200 

437 

1100 

Material. 

Concrete,  6 parts;  shingle;  1 
part  sand ; 1 part  concrete . . 

((  (( 

Earth  (clay,  chalk,  stones,  and 
brick) 

Same  

Earth  

Sand 

Concrete,  granite  and  con- 
crete, broken  granite  

Sand 

Soft  rock  and  sand 

Stiff  marsh  clay 

Clay  half,  sand  half.. 

Earth  

(( 

Concrete  or  brick 

Stone  masonry 

\i 

Place  and  Date. 

Dungeness,  1881 

“ 1881 

“ 1881 

“ 1881 

“ 1881 

“ 1881 

“ 1881 

Shoeburyness,  Aug.,  1883 

Spezia,  May,  1880  

“ March,  1881 

Shoeburyness,  1865 

Calais 

Shoeburyness  and  New  Haven 

t(  ^ U (i 

i(  ((  (« 

(t  ((  (( 

4(  t<  it 

((  ti  ti 

t(  ti  tt 

tt  it  it 

* This  table  is  taken  from  “ Report  of  the  Board  on  Fortifications  or  Other  Defences,”  1886. 


164 


APPENDIX. 

The  following  thicknesses  of  parapets  were  prescribed  for  German 
fortifications  in  1884: 


Kinds  of  Guns. 

Thickness. 

Snow  well 
packed. 

Earth. 

Masonry. 

Wr’ght-iron 
and  Besse- 

“'mer'^eel.' ' 

Small-arms  and  shrapnell. . 
Field  guns 

Feet. 

2 to  3 

10  to  12 
17  to  23 
33  to  40 

Feet. 

3 

4.5  to  5 

Inches. 
0.25  to  0.50 
4.5  to  5.0 

Feet. 

6 

26 

Siege  and  fortress  guns 

Ship’s  f^iins 

■ *' 

From  experiments  made  by  the  Germans  it  was  found  that  chilled 
projectiles  penetrate  rolled  iron  from  f to  | diameters;  that  small-arms 
will  penetrate  9"  of  oak  and  10"  of  fir. 


APPENDIX. 


165 


APPENDIX  II. 


FEONTIEE  AND  INTEEIOE  FOETIFICATIONS 
OF  FEANCE,  GEEMANT,  ITALY,  AUSTEIA- 
HUNGAEY,  AND  EUSSIA  IN  EUEOPE. 

FRANCE. 

Since  the  war  of  1870-71,  the  defensive  frontier  of  France 
has  been  remodelled.  Many  of  the  old  works  have  been 
abandoned,  others  ameliorated,  and  new  works  constructed 
in  positions  of  modern  strategical  importance. 

The  Belgian  Frontier. — This  frontier  presenting  no 
natural  obstacle,  a line  of  strong  works  has  been  constructed 
along  it  by  the  amelioration  of  the  old  fortifications.  De- 
tached forts  have  been  placed  around  the  most  important 
*centres,  converting  them  into  intrenched  camps.  The  first 
line  of  defence  consists  > of  four  groups  of  works  : Dun- 
kerque^  Lille^  Valenciennes^  and  Mauheitge.  The  first 
group  Dunkerque,  Bergues,  and  Gravelines.  and 

is  being  strengthened  by  the  construction  of  detached  forts. 
The  second,  Lille,  which  is  to  have  a cordon  of  forts,  Aire 
and  Douai.  The  third,  Valenciennes,  which  is  to  have  a 
cordon  of  forts  (some  already  constructed),  Bouchain, 

and  Quesnoy.  The  fourth,  Mauheuge,  which  has  a cordon 
of  forts,  Landrecies,  Hirson,  a?id  Bocroy.  In  the  second 
line,  on  the  river  Somme,  are  the  citadel  at  Amiens,  and 
the  fortresses  of  Peronne  and  Ham  / farther  south,  tlie 
strategic  triangle  of  La  Fere,  Laon,  Soissons.  This  tri- 
angle, when  the  fortifications  about  tliese  places  are  com- 
pleted, will  form  an  immense  intrenched  camp  ; the  base  of 
armies  operating  in  the  north  of  France.  Rheims,  further 
■south,  is  also  an  intrenched  camp  with  detached  forts. 

The  German  Frontier. — The  defensive  works  along  this 
frontier  are  constructed  along  the  river  Meuse  from  Givet  to 
Tout,  and  thence  along  the  Moselle  to  Belfort.  Givet  is  a 


166 


APPEN-DIX. 


email  fortress  of  minor  importance.  Mezieres  is  a fortress 
which  bars  the  valley  of  the  Meuse,  and  occupies  an  important 
railroad  junction.  Verdun  is  an  intrenched  cam.p  on  the 
railroad  from  Metz  to  Paris.  Toul  is  an  intrenched  camp 
on  the  railroad  from  Strasburg  to  Paris.  Verdun  and 
Toul  are  connected  by  a line  of  forts.  Epinal  is  an  in- 
trenched camp  on  the  upper  Moselle.  Belfort  is  a large  in- 
trenched camp  near  the  frontier  of  Switzerland.  Epinal 
and  Belfort  are  connected  by  a line  of  forts.  Montmedy 
and  Longwy  are  small  fortresses  along  the  railroad  from 
Luxemburg  and  Thionville  to  Mezieres.  In  the  rear  of  this 
frontier  line  are  the  intrenched  camps  of  Langres^  Diyon^ 
and  Besanqon.  The  intrenched  position,  Belfoif  Epnial^ 
Langres,  Dijon  and  Besangon^  will  form  the  base  of  an 
army  operating  from  the  south  along  this  frontier. 

The  Italian  and  Swiss  Frontiers. — The  line  of  the 
Alps  is  defended  by  numerous  small  forts  in  the  passes,, 
supported  in  the  rear  by  the  intrenched  camps  of  Besangony 
Lyons ^ and  Grenoble. 

Spanish  Frontier. — The  line  of  the  Pyrenees  is  defended, 
by  numerous  old  works  which  have  been  only  slightly 
changed  since  the  time  of  Yauban.  The  principal  ones 
are  those  at  Perpignan.^  on  the  Mediterranean  side,  and 
Bayonne  on  the  Atlantic. 

Sea-coast  Fortifications. — The  principal  sea-coast  works 
are,  on  the  English  Channel  : Cherbourg.^  St.  Malo^  and 
Eame ; on  the  Atlantic:  Rochefort.,  Lor  lent.,  Brest.,  La 
Rochelle.,  Oleron^  and  Belle  Isle  / on  the  Mediterranean : 
Toidon  and  Antibes. 

The  capital,  Paris,  the  centre  of  the  defensive  system,, 
has  been  converted  into  an  immense  intrenched  camp,  hav- 
ing a cordon  of  forts  at  a distance  of  about  nine  miles  from 
the  city. 

GERMANY. 

T^early  all  of  the  existing  fortifications  of  Germany  have 
either  been  built  or  ameliorated  since  1870.  The  intrenched 
camps  have  usually  an  enceinte  surrounded  by  a line  of  de- 
tached forts  at  a distance  of  four  to  five  miles  from  the 
enceinte,  and  from  two  to  two  and  a half  miles  from  each 
other;  between  these  forts  are  constructed  intermediate 
works  and  batteries. 

The  Western  Frontier. — The  main  line  of  defence 
against  an  army  coming  from  the  west  is  along  the  river 
Rhine ; but  beyond  this  are  the  intrenched  camp  of  Metz, 
and  \X\^  fortress  of  Thionville  on  the  Moselle,  the  tete-de- 


APPEIfDIX. 


167 


jpont  at  Saar  Louis^  and  the  old  fortress  of  Bitche.  On  the 
Rhine  are  the  fortress  and  tUe-de-jpont  of  Neu  Brisach^ 
the  intrenched  camp  of  Strasburg,  the  tete-de-pont  of 
Germersheim^  the  intrenched  camp  of  Mainz^  with  Castel 
on  the  opposite  side  of  the  river ; forts  Alexander^  Fran- 
qois^  and  Ehr  enbre  it  stein  ^ at  Coblenz  / the  intrenched  camp 
at  Cologne^  with  Deutz  on  the  opposite  bank,  a iete-de-pont 
at  Dusseldorf^  and  two  forts  protecting  the  river-crossing  at 
Wesel.  These  works  control  all  the  principal  bridges  across 
the  Rhine  from  Bale  to  Wesel.  On  the  east  bank  of  the 
Rhine  is  the  intrenched  camp  of  Rastadt. 

Southern  Frontier. — On  the  Danube  are  the  intrenched 
camps  of  JJlm  and  Ingolstadt ^ on  the  Elbe,  the  fort  of 
Kunig stein  • and  in  Prussia,  the  old  fortified  places  of 
Glatz  and  JEeisse. 

Eastern  Frontier. — This  frontier  is  now  protected  by 
three  intrenched  camps  of  the  first  order.  KOnigsberg  in 
eastern  Prussia,  Thorn  on  the  Yistula,  and  Posen  on  the 
Warthe.  In  addition  to  these  are  tetes-depont  at  Marten- 
bttrg,  on  the  Nogat;  Perschau  and  Grandenz  on  the  Yis- 
tula, and  the  fortress  of  Glogau  on  the  Oder. 

The  capital,  Berlin^  is  not  fortified,  but  its  approaches 
are  defended  by  the  intrenched  camp  at  Magdeburg ; the 
old  fortress  at  Torgau^  on  the  Elbe,  and  the  intienchcd 
camp  of  Cilstrin^  on  the  Oder.  An  intrenched  camp  is 
also  being  constructed  at  Spandau,  in  the  immediate  vicin- 
ity of  Berlin. 

Sea-coast  Fortifications. — The  principal  naval  port  on 
the  North  Sea  is  that  of  Wilhelmshaven^  and  on  the  Baltic 
that  of  Kiel^  protected  by  the  works  of  Friedrichsort.  In 
addition  to  these,  on  the  North  Sea,  are  the  works  Cuxharen 
at  the  mouth  of  the  Elbe,  and  Geestem.unde  at  the  mouth 
of  the  Weser;  on  the  Baltic,  Sonderburg-Duppel^  Stral- 
sund;  Travemunde,  at  the  entrance  of  the  port  of  Lubeclc', 
Swinemunde,  at  the  mouth  of  the  Oder  / Kolberg^  Danzig^ 
Pillau,  and  Memel, 

ITALY. 

Italy  possesses  a large  number  of  old  fortresses  and  forti- 
fied towns ; the  only  ones,  however,  of  modern  strategical 
importance  are  Alexandria^  Casale^  Bologna^  Captua^ 
Legnano^  Mantua^  Peschiera^  Placencia,  Pizzeghettone, 
Yerona^  and  Rome.  Rome  has  been  converted  into  an  in- 
trenched camp  by  the  construction  of  a cordon  of  forts,  and 
the  fortifications  of  Capua  are  being  ameliorated,  but  none 


168 


APPEJSDIX. 


of  the  other  places  can  be  considered  as  strong  places  ac- 
cording to  the  modern  idea. 

In  the  last  few  years  much  attention  has  been  paid  to  the 
construction  of  works  in  the  passes  of  the  Alps,  to  bar  the 
advance  of  armies  coming  from  France  and  Austria.  The 
principal  works  of  this  class  are  those  of  Fort  Bard^  Exille, 
Fenestrelle^  Yenadio,  Monte  Argentera.  Ventimiglia,  on 
the  French  frontier,  and  Bivoli  on  the  Austrian. 

Sea-coast  Fortifications. — Particular  attention  has  been 
paid  to  the  reconstruction  of  the  sea-coast  fortifications. 
Spezia  on  the  Mediterranean,  is  the  principal  naval  port, 
and  is  being  thoroughly  fortified  ; work  is  also  going  on  at 
Genoa,  Gaeta,  Porto-Ferraio  on  the  island  of  Elba  ; the 
Island  of  Maddalena,  and  Messina,  on  the  Atlantic; 
Ancona  Venice,  and  Tarento,  on  the  Adriatic.  Givita 
Vecchia  is  also  a fortified  port. 

AUSTRIA-HUNGARY. 

Austria-Hungary  has  numerous  old  fortifications,  some  of 
which  have  been  ameliorated.  The  great  extent  of  assail- 
able frontier  making  a thorough  defence  impossible,  the 
Austrian  engineers  have  limited  themselves  generally  to 
the  construction  of  small  works,  simply  intended  to  im- 
pede invasion  by  obstructing  the  principal  lines  of  com- 
munication leading  into  the  country. 

Bavarian  Frontier. — There  is  a fortress  at  Kilf stein  on 
the  Inn  ; a fort  at  Pass  Liieg,  south  of  Salzburg,  and  an 
old  intrenched  camp  at  Linz 

Saxon  and  Prussian  Frontier. — On  the  Elbe  is  the 
intrenched  camp  at  Theresienstadt,  the  old  fortifications 
of  Josephstadt  and  ILdniggratz  on  the  Elbe,  and  on  the 
March  an  intrenched  camp  at  Olmutz. 

Russian  Frontier. — The  fortifications  consist  of  in- 
trenched camps  at  Cracow,  on  the  Yistula,  and  2X  Przemysl, 
on  the  San,  a tributary  of  the  same.  In  the  second  line 
is  the  fortress  Epevies,  on  the  Tarcza,  a tributary  of  the 
Theiss.  The  intrenched  camp  at  Przemysl,  for  which 
5,500,000  florins  have  been  appropriated,  will,  when  com 
pleted,  be  the  strongest  fortification  of  Austria. 

Roumanian  Frontier. — There  are  numerous  old  fortified 
places  in  Transylvania,  the  principal  ones  of  which  are  Kron^ 
stadt  and  Orsova ; in  Hungary,  on  the  Danube,  is  the  in- 
trenched camp  at  Komorn,  and  fortifications  at  Peter- 
wardein ; on  the  Maros,  Karlshurg  and  Arad;  on  the 


APPENDIX. 


1G9 


Drave,  EszeJc  ; in  Croatia  and  Dalmatia,  on  the  Save,  Brod^ 
Gradiska^  and  Karlstadt, 

The  Italian  Frontier  is  protected  by  numerous  forts 
constructed  at  the  passes  through  the  Alps. 

Sea-coast  Fortifications. — The  principal  naval  port  is 
Pola^  on  the  Adriatic ; fortifications  also  exist  at  Trieste^ 
Fiume,  Zara^  Sehenico,  Spalatro,  Bagusa,  lately  aban- 
doned, and  the  island  of  Lissa. 

The  capital,  Vienna^  is  not  fortified. 

RUSSIA  IN  EUROPE. 

Prussian  and  Austrian  Frontier. — The  Polish  posses- 
sions of  Russia  are  protected  by  three  strongly  fortified  places  : 
Novo- G ear giemk  (Modlin),  at  the  junction  of  the  Bug  and 
Vistula ; Warsaw^  the  capital  of  Poland,  and  an  important 
railroad  centre  on  the  Vistula ; and  Ivangorod^  on  the  same 
river.  In  rear  of  this  line  on  the  Bug  is  the  strongly  fortified 
place  of  Brest- Litovsk,  In  the  rear  of  these  frontier  for- 
tresses are  Bjelostok^  a small  fortress  at  the  junction  of  the 
railways  from  Warsaw  to  St.  Petersburg,  and  Kbnigsberg 
to  Brest-Litovsk  ; the  intrenched  camp  of  Kovno^  on  the 
JN^iemen,  the  citadel  of  Wilna ; the  intrenched  camp  of 
Bunaberg^  on  the  Buna  ; the  old  fortifications  of  Smolensky 
on  the  Dnieper ; the  old  fortress  of  Luzk.  and  the  fortifica- 
tions in  process  of  construction  at  Botibno^  on  the  railways 
leading  from  Poland  and  Galicia  towards  Kiev ; and  the  in- 
trenched camp  of  Kiev  on  the  Dnieper. 

Roumanian  Frontier. — In  the  vicinity  of  this  frontier 
are  the  old  fortresses  of  Kamenez-Podolsk^  Chotin^  Bend- 
ery^ and  Tiraspol. 

Sea-coast  Fortifications. — The  principal  naval  ports  on 
the  Baltic  are  Helsingfors.,  protected  by  the  fortifications  on 
the  Sveaborg  Islands,  and  the  harbor  of  Kronstadt ; in 
addition  to  these  are  the  forts  Hang'6.,  Puotsinscdmi., 
Fredrikshamn^  Viborg,  and  Baltischport^  on  the  Gulf  of 
Finland;  and  Riga^em  the  Gulf  of  Riga,  is  protected  by  the 
fortifications  of  Bunamunde. 

The  principal  naval  port  on  the  Black  Sea  \!$>  Nikolaifsk., 
.protected  by  the  works  of  Otschakow  and  Kinburn ; in 
.addition  there  are  the  works  of  Akkerman.,  Sebastopol.,  and 
the  fortifications  on  the  Kertch  Strait. 

The  Caucasus. — There  are  numerous  old  fortifications 
between  the  Black  and  Caspian  Seas.  The  most  important  of 
these  are  Kars  and  Alexandropol. 


170 


APPEi^DIX. 


APPENDIX  III. 


BOOKS  OF  KEFEKENCE. 

The  following  list  comprises  a few  of  the  many  valuable- 
works  upon  permanent  fortifications,  and  its  allied  branches 
of  Military  Engineering. 

In  the  books  mentioned  will  be  found  references  to  many 
others  treating  fully  upon  the  different  branches  of  the  sub- 
ject. 

It  is  not  considered  necessary  to  repeat  the  names  of  all 
the  works  referred  to  in  the  text;  nor  to  enumerate  the- 
writings  of  Yauban,  Cormontaigne,Coehoorn,Montalembert, 
Chasseloup,  La  Chiche,  Virgin,  Choumara,  Dufour,  Noizet, 
and  other  standard  authors. 

Adams,  Capt.  H.  M. : Report  on  Trial  of  Chilled-iron  Armor  at 
Spezia.  Washington,  1886. 

Barnard,  Gen.  J.  G. : Dangers  and  Defences  of  New  York.  New 
York,  1859. 

— — Notes  on  Sea-coast  Defence.  New  York,  1861. 

Wright  & Michie:  Fabrication  of  Iron  for  Defensive  Purposes, 

with  Supplement.  Washington,  1871. 

Barnes  : Submarine  Warfare.  New  York,  1869. 

Bixby,  Capt.  W.  H. : Report  on  Fortification  and  Ordnance,  pub- 
lished in  “ Engineering  News.”  1885. 

Brialmont:  Etudes  sur  la  Defence  des  Etats  et  de  la  Fortification. 
Paris,  1863. 

Traite  de  Fortification  Polygonal.  Paris,  1869. 

La  Fortification  a Fosses  secs.  Paris,  1872. 

— — Etudes  sur  la  Fortification  des  Capitales  et  I’investissement  des. 
Camps  Retranches.  Paris,  1873. 

La  Fortification  du  Temp  Present.  Brussels,  1885. 

Craighill:  Guns  Afloat  and  Guns  Ashore.  Essay ons  Club  Paper, 
No.  6.  1868. 

Delafield:  Report  on  Art  of  War  in  Europe  in  1854-56.  Washing- 
ton, 1860. 

Douglas:  Observations  on  Modern  System  of  Fortification.  London, 
1859. 

Fortifications  of  To-day:  Translated  from  Italian.  Washington,. 
1883. 


APPENDIX. 


171 


Fraser:  The  Attack  of  Fortresses  of  the  Future.  London,  1877. 
Girard:  Traite  d’application  Tactiques  de  la  Fortification.  Paris,. 
1874. 

Gillmore:  Siege  of  Fort  Pulaski.  Washington,  1864. 

Goodrich:  Report  of  British  Military  and  Naval  Operations  in 
Egypt.  Washington,  1885. 

Giese:  Constructions  of  Iron  as  applied  to  Fortification.  Washing- 
ton, 1867. 

Griffin:  Our  Sea-coast  Defences.  New  York,  1885. 

Humfrey,  J.  H.:  Essay  on  Modern  Systems,  etc.  London,  1838. 
King,  Major  W.  R. : Armor  Plating  for  Land  Defences.  Washing- 
ton, 1870. 

Torpedoes.  Washington,  1866. 

Economy  in  Sea-coast  Defences;  Essayons  Club  Paper,  No.  19. 

1871. 

King,  J.  W. : European  Ships  of  War.  Washington,  1877. 

.Kunka:  Die  Panzerthurme.  Vienna.  1876. 

Lendy:  A Treatise  on  Fortification.  London,  1862. 

Mangin:  Memoire  sur  la  Fortification  Polygonal;  construite  in 
Allemagne  depuis  1815.  Paris,  1851. 

Die  Polygonal  Befestigung.  Leipzig.  1855. 

Maguire:  Attack  and  Defence  of  Coast  Fortifications.  New  York, 
1884. 

Prevost,  F. : Etudes  Historiques  sur  la  Fortification.  Paris,  1869. 
Prevost  de  Vernois:  De  la  Fortification  depuis  Vauban.  Paris,  1861. 
Ratheau:  Traite  de  Fortification.  Paris,  1866. 

Attaque  et  Defence  des  Places  Fortes.  Paris,  1877. 

Report  of  Board  on  Fortification  or  other  Defences.  Washington, 
1886. 

Of  Select  Committee  on  Ordnance  and  War  Ships.  Washing- 
ton, 1886. 

With  Reference  to  Progress  in  Construction  of  Fortifications  for 

Dockyards,  etc.  London,  1867. 

Of  Committee  on  Gibraltar  Shield.  London,  1868. 

Upon  Practice  in  Europe  with  Heavy  Guns.  Prof.  Paper,. 

Corps  of  Engineers,  No.  25.  Washington,  1883. 

Record  of  Experimental  Firing  at  Fort  Monroe.  Washington,  1870.. 
Schueler  Leitfaden  ftir  den  Unterricht  in  der  Befestigung,  etc. 
Berlin,  1884. 

Schiitz,  J.  von:  Experiences  de  Bucharest.  Brussels,  1886. 

Sellon,  Maurice  de:  Various  Writings.  Paris,  1845  et  seq. 

Sleeman:  Torpedoes  and  Torpedo  Warfare.  Portsmouth,  England,. 
1880. 

Stotherd:  Notes  on  Torpedoes  Offensive  and  Defensive  (Reprint). 
Washington,  1872. 

Totten:  Casemate  Embrasures.  Washington,  1857. 

Tripier:  La  Fortification  de  son  Histoire.  Paris,  1886. 

Tenot:  Paris  et  ses  Fortifications.  Paris,  1880, 

Very:  The  Navies  of  the  World.  Washington,  1880. 

The  Development  of  Armor  for  Naval  Use.  Annapolis,  1883. 

Viollet-le-duc  : Annals  of  a Fortress.  Boston,  1876. 

Von  Schelliha:  Treatise  on  Coast  Defence,  etc.  London,  1868. 
Woolwich:  Text  Book  on  Fortification.  London,  1877. 

Zastrow:  Histoire  de  la  Fortification  Permanente.  Paris,  1866. 


V- 


\ 


K . 


't 


■ * ’.{I  ' i 

• ■ ( u 


I 


1^, 


''  . 


7 


'M 


7 .' 


< ■ \ 


■\ 


M 


i'' 

fc' 


■{■ 


.'-I'-;;: 

i ■ -V 


\ 


.W- 


Plate  1. 


Plate  2. 


PlrtTV 


S^cctCorv  orv  C 2?. 


^ Co4i, 


^3^0  Cu^t4>  ^er,rf£j  o/^ 0 SS^^O 
2o.€»oO  » » » £jrc&^^>€££€^rv,  ^ 00-^  gooo. 

‘fZ  J^la;^rrri^  ^4^  Jor ^CMJe>r4€^  C>vU^, 

2 0rrfK^^h£  *^T*or9^  ^ 0 /X09.nm  3000 

S0  *X^5y«^  ^ J //  So  9/0  ' 

C2>m/d>n^Cr*^CAA  i fSOp-^ 


0 S^oo'yoh. 


/ 


FJiite  3.. 


I : 


-4-  - ■ r 

_i 

1 

1 1 

Lil. 

! 

\ t 

1 

i 

' *! 

i 

r 

i 

s 1 

i 1 

n 

Q:  C 

*! 

f 

V 

s P 

i ! 

^ i 

1 

.1 

! 

1 

/' 

is:  ...  j 
1 

^j_..y  ...| 

1 

|---'| 

'.-90.'.. 1 

, . m-5_^ 

' J 

1 

^ - -1 

1 ) 

- 

•i 

) 

yi. 

1) 

iJL 

A'- 

JI22y  1 

3 


Plate  5, 


• Jl 


P]  al  e (i. 


Plate  7. 


IFF  CARRIAGE 

FOR  12%  TON  GUN. 


Jca.U  </  /-M. 

^ I ! 


^ ^ 


Plate  7. 


Plate  8. 


Ftq.03  Fig\62  ji 


PI  ate  H 


y '4 


Plate  0 


Plate  lO. 


r 


2 


^■e<ctc4my  OTZf  torve/  ^ 


7 


2f  2 


JTt^  5 


Plate  11, 


Plate  11a. 


Plate  12. 


Scale  for  Fi^.  3, 


=J=f 


J 


Plate  12. 


Plate  13 


I 


^rtir 


too 


Scale  for  Fig.  2. 


Plate  13, 


2?.F 


Plate  14. 


Plaite  15. 


S ection  oil  M Fig3^ 


k 1 

, N 

4M 

II II 

F^W 

B 

1 M 1 

BJ 

B 

[i  1 1 1 

Nr* 

<•(« 

1 1 II  1 

•III  M. J 

iS  ection  on  EF,  Fi^.  % 


Section  on  GH.Fi^.  2 

«»v 

^ ' '7^ 


on  CD  Ft^.  2 


S ection  on  KL  Fi^.  2. 


tScalc  Jbr  T^tg  2 

~i.  J.  L 


-X  ,i 


Plaite  15. 


Plate  le. 


XV. Po->vd4i.r  JH/J^^'^ctU/. 

b.  — Hocmt/. 

X>.—Se>rvvC€/  Joivdor  JH/r^fr'^i7i/e< 

^ L/  a^o/'ato7'i/iJj  to7’C(i  S Jul/€^7’J. 

.€/.—  S tore/  Jtoow/i. 

J\^  Qtcwrte'7-J. 


c^Ze>  of  PLol7u 


Plat 


IB 


e Ifi- 


Plate  18 


Plate  iS. 


Plate  19 


Plate  19, 


*r-  ■ > ^ • r , , , . . ^ ^ ^ H n ^ 

DISAPPEARING  TURRET  FOR  IMACHINE  GUN. 

ri^  5. 


DISAPPEARING  TURRET  FOR  MACHINE  GUN. 

ny  4. 


FIXED  TURRET  CAPONNIERE  MACHINE  GUNS. 


REVOLMNG  TURRET  CAPONNIERE 

rOR  MACHINE  GUNS. 

CMipn^d ytr  at  <*.ny»j  of  Diich.«4. 

riyf. 


BOOKS  FOB 


ARMY  AND  NAVY  OFFICERS 

PUBLISHED  BY 

JOHN  WILEY  & SONS. 


ORDNANCE  AND  GUNNERY. 

For  the  use  of  the  Cadets  of  the  U.  S.  Military  Academy.  Hy 
Captain  Henry  Metcalf,  Ordnance  Department,  U.  S.  Army 
Instructor  of  Ordnance  and  Gunnery,  U.S.M.  A.  13mo,  500  pp., 
cloth,  with  separate  atlas  containing  350  cuts,  . . $5.00 

MODERN  FRENCH  ARTILLERY. 

The  St.  Chamond,  De  Bange,  Canet  and  Hotchkiss  systems,  with 
illustrations  of  French  War  Ships,  By  James  Dredge.  4to,  half 
morocco,  .......  $20.00  net 

HANDBOOK  OF  PROBLEMS  IN  DIRECT  FIRE. 

By  James  M.  Ingalls,  Captain  First  Artillery,  U.  S.  A.  8vo, 
cloth,  . . ■ . . . . . . $4.00 

BALLISTIC  TABLES. 

Eeprinted  from  the  Handbook  for  West  Point  Cadets.  By 
("apt.  Jas.  M.  Ingalls.  8vo,  cloth,  ....  $1.50 

SUBMARINE  MINES  AND  TORPEDOES. 

As  applied  to  Harbour  Defense.  By  John  Townsend  Bucknill, 
Honorary  Lieutenant-Colonel  (late  Major  Royal  Engineers) 
Reserve  of  Officers.  With  illustrations.  8vo,  cloth,  . $4.00 

PRACTICAL  SEAMANSHIP. 

By  John  Todd,  Master  Mariner,  and  W.  B.  Whall,  Extra  Master 
Younger  Brother  Trinity  House.  Royal  8vo,  full  cloth,  with 
243  Illustrations  and  Diagrams,  «...  $7.50 

NOTES  ON  MILITARY  HYGIENE. 

For  Officers  of  the  Line.  A Syllabus  of  Ijectures  at  the  U.  S. 
Infantry  and  Cavalry  School.  By  Alfred  A.  Woodhull,  Major 
of  Medical  Dep’t.,  Bvt.  Lt.  Col.  U.  S.  Army.  12mo,  morocco, 

S3.50 

SIMPLE  ELEMENTS  OF  NAVIGATION. 

By  Lucien  Young,  U.  S.  Navy.  Pocket-book  form.  New 
edition,  revised  and  enlarged,  ....  $2.50 


THE  SOLDIERS*  FIRST  AID  HANDBOOK. 

Comprising-  a Series  of  Lectures  to  Members  of  the  Hospital 
Corps  and  Company  Bearers.  By  William  D.  Dietz,  Late  Cap- 
tain and  Assistant  Surgeon  U.  S.  Army.  18mo,  morocco,  $1.35 


PERMANENT  FORTIFICATIONS. 

By  Prof.  D.  H.  Mahan,  Revised  and  brought  up  to  date  by  Col. 
James  Mercur,  U.  S.  Military  Academy,  West  Point.  Numer- 
ous plates,  1887.  8vo,  half  morocco,  . . . $7.50 

ELEMENTS  OF  THE  ART  OF  WAR. 

By  James  Mercur,  Professor  of  Civil  and  Military  Engineering, 
United  States  Military  Academy.  Illustrated  with  full-page 
and  folding  plates.  Third  edition.  8vo,  cloth,  . . $4.00 

PRACTICAL  MARINE  SURVEYING. 

By  Harry  Phelps,  U.  S.  Navy.  8vo,  cloth,  . . $3.50 

AN  ABRIDGEMENT  OF  MILITARY  LAW. 

By  Col.  W.  Winthrop,  Deputv  Judge  Advocate-General,  U.S. 
Army,  late  Professor  of  Law,  U.  S.  Military  Academy.  Second 
and  revised  edition.  13mo,  red  cloth,  . . . $3.50 

A MANUAL  FOR  COURTS-MARTIAL. 

Prepared  by  Lt.  Arthur  Murray,  1st  Artillery,  late  Acting 
Judge  Advocate-General,  U.  S.  A.  Third  edition.  18mo,  mo- 
rocco, flap,  .......  $1.50 

CAVALRY  OUT-POST  DUTIES. 

By  F.  De  Brack,  translated  from  the  French  (third  edition,  1863) 
by  Major  Camillo  C.  C.  Carr,  8th  Cavalry,  U.  S.  A.  18mo,  mo- 
rocco, flap,  .......  $3.00 

GUNNERY  FOR  NON-COMMISSIONED  OFFI- 
CERS. 

Compiled  by  Lt.  Adelbei’t  Cronkhite,  4th  Artillery,  with  Ballis- 
tic Tables,  by  Capt.  James  M.  Ingalls,  1st  Artillery,  18mo, 
morocco,  flap,  ......  $3.00 

ART  OF  SUBSISTING  ARMIES  IN  WAR. 

By  Capt.  H.  G.  Sharpe,  U.  S.  A. 

Morocco,  ........  $1.50 

THE  ARMY  OFFICER’S  EXAMINER. 

By  Lt.  Col.  W.  H.  Powell,  U.  S.  A.  12mo,  cloth,  . $4.00 

ELEMENTARY  NAVAL  TACTICS. 

By  Commander  Wm.  Bainbridge-Hotf,  U.  S.  N.  8vo,  cloth,  $1.50 


ATTACK  OF  FORTIFIED  PLACES. 

Including  Siege-Works,  Mining  and  Demolitions.  By  James 
Mercur,  U.  S.  M.  A.,  Professor  of  Civil  and  Military  Engineering. 
13mo,  cloth,  .......  $3.00 

TEXT-BOOK  OF  ORDNANCE  AND  GUNNERY. 
For  the  use  of  the  Cadets  of  U.  S.  M.  A.  By  Capt.  Lawrence  L. 
Bruff,  U.  S.  A.  8vo,  cloth $6.00 


HANDBOOK  FOR  LIGHT  ARTILLERY. 

By  A.  B.  Dyer,  First  Lieut.  Fourth  U.  S.  Artillery, 
cloth,  ........ 


12mo, 

$3.00 


SHORT-TITLE  CATALOGUE 

OP  THE 

PUBLICATIONS 

OF 

JOHN  WILE  Y & SONS, 

New  York. 

London:  CHAPMAIST  & HALL,  Limited, 
ARRANGED  UNDER  SUBJECTS. 

Descriptive  circulars  sent  on  application. 

Books  marked  w'ith  an  asterisk  are  sold  at  net  prices  only. 

All  books  are  bound  in  cloth  unless  otherwise  stated. 


AGRICULTURE. 

Cattle  Feeding— Diseases  of  Animals — Gardening,  Etc. 


Armsby’s  Manual  of  Cattle  Feeding 12mo,  |1  75 

Downing’s  Fruit  and  Fruit  Trees 8vo,  5 00 

Kemp’s  Landscape  Gardening 12mo,  2 50 

Stockbridge’s  Rocks  and  Soils .....8vo,  2 50 

Lloyd’s  Science  of  Agriculture 8vo,  4 00 

Loudon’s  Gardening  for  Ladies.  (Downing.) 12mo,  1 50 

Steel’s  Treatise  on  tbe  Diseases  of  the  Ox 8vo,  6 00 

“ Treatise  on  tbe  Diseases  of  the  Dog 8vo,  3 50 


Grotenfelt’s  The  Principles  of  Modern  Dairy  Practice.  (Woll.) 

12mo,  2 00 

ARCHITECTURE. 

Building — Carpentry— Stairs,  Etc. 


Berg’s  Buildings  and  Structures  of  American  Railroads 4to,  7 50 

Birkmire’s  Architectural  Iron  and  Steel 8vo,  3 50 

Skeleton  Construction  in  Buildings 8vo,  3 00 

1 


Birkmire’s  Compound  Riveted  Girders 8vo,  |2  OU 

“ American  Theatres— Planning  and  Construction. 8vo,  3 00 

Carpenter’s  Heating  and  Ventilating  of  Buildings 8vo,  3 00 

Freitag’s  Architectural  Engineering 8vo,  2 50 

Kidder’s  Architect  and  Builder’s  Pocket-book Morocco  flap,  4 00 

Hatfield’s  American  House  Carpenter 8vo,  5 00 

“ Transverse  Strains 8vo,  5 00 

Monckton’s  Stair  Building — Wood,  Iron,  and  Stone 4to,  4 00 

Gerhard’s  Sanitary  House  Inspection 16mo,  1 00 

Downing  and  Wightwick’s  Hints  to  Architects 8vo,  2 00 

“ Cottages 8vo,  2 50 

Holly’s  Carpenter  and  Joiner 18mo,  75 

Worcester’s  Small  Hospitals-  -Establishment  and  Maintenance, 
including  Atkinson’s  Suggestions  for  Hospital  Archi- 
tecture  12mo,  1 25 

The  World’s  Columbian  Exposition  of  1893 4to,  2 50 


ARMY,  NAVY,  Etc. 

Military  Engineering — Ordnance — Port  Charges,  Etc. 

Cooke’s  Naval  Ordnance 8vo,  $12  50 

Metcalfe’s  Ordnance  and  Gunnery 12mo,  with  Atlas,  5 00 

Ingalls’s  Handbook  of  Problems  in  Direct  Fire 8vo,  4 00 

“ Ballistic  Tables 8vo,  1 50 

Bucknill’s  Submarine  Mines  and  Torpedoes 8vo,  4 00 

Todd  and  Whall’s  Practical  Seamanship 8vo,  7 50 

Mahan’s  Advanced  Guard 18mo,  1 50 

“ Permanent  Fortifications.  (Mercur.).8vo,  half  morocco,  7 50 

Wheeler’s  Siege  Operations 8vo,  2 00 

Woodhull’s  Notes  on  Military  Hygiene 12mo,  morocco,  2 50 

Dietz’s  Soldier’s  First  Aid 12mo,  morocco,  1 25 

Young’s  Simple  Elements  of  Navigation. .12mo,  morocco  flaps,  2 50 

Reed’s  Signal  Service 50 

Phelps’s  Practical  Marine  Surveying 8vo,  2 50 

Very’s  Navies  of  the  World 8vo,  half  morocco,  3 50 

Bourne’s  Screw  Propellers 4to,  5 00 

2 


Hunter’s  Port  Charges 8vo,  half  morocco,  $13  00 

* Dredge’s  Modern  French  Artillery 4to,  half  morocco,  20  00 

“ Record  of  the  Transportation  Exhibits  Building, 
World’s  Columbian  Exposition  of  1893.. 4to,  half  morocco,  15  00 

Mercur’s  Elements  of  the  Art  of  War 8vo,  4 00 

“ Attack  of  Fortified  Places 12mo,  2 00 

Chase’s  Screw  Propellers 8vo,  3 00 

Winthrop’s  Abridgment  of  Military  Law 12mo,  2 50 

De  Brack’s  Cavalry  Outpost  Duties.  (Carr.). . . .18mo,  morocco,  2 00 

Cionkhite’s  Gunnery  for  Non-com.  Officers 18mo,  morocco,  2 00 

Dyer’s  Light  Artillery 12mo,  3 00 

Sharpe’s  Subsisting  Armies 18mo,  1 25 

“ “ “ 18mo,  morocco,  1 50 

Powell’s  Army  Officer’s  Examiner 12mo,  4 00 

Hoff’s  Naval  Tactics 8vo,  1 50 

Bruff’s  Ordnance  and  Gunnery 8vo,  6 00 

ASSAYING. 

Smelting — Ore  Dressing— Alloys,  Etc. 

Furman’s  Practical  Assaying 8vo,  3 00 

Wilson’s  Cyanide  Processes 12mo,  1 50 

Fletcher’s  Quant.  Assaying  with  the  Blowpipe..  12mo,  morocco,  1 50 

Ricketts’s  Assaying  and  Assay  Schemes 8vo,  3 00 

* Mitchell’s  Practical  Assaying.  (Crookes.) 8vo,  10  00 

Thurston’s  Alloys,  Brasses,  and  Bronzes 8vo,  2 50 

Kuuhardt’s  Ore  Dressing 8vo,  1 50 

O’Driscoll’s  Treatment  of  Gold  Ores 8vo,  2 00 

ASTRONOMY. 

Practical,  Theoretical,  and  Descriptive. 

Michie  and  Harlow’s  Practical  Astronomy 8vo,  3 00 

White’s  Theoretical  and  Descriptive  Astronomy 12mo,  2 00 

Doolittle’s  Practical  Astronomy 8vo,  4 00 

Craig’s  Azimuth 4to,  3 50 

Gore’s  Elements  of  Geodesy .8vn,  2 50 


3 


BOTANY. 

Gardening  for  Ladies,  Etc. 


Westermaier’s  General  Botany.  (Schneider.) 8vo,  $2  00 

Thome’s  Structural  Botany 18mo,  2 25 

Baldwin’s  Orchids  of  New  England 8vo,  1 50 

Loudon’s  Gardening  for  Ladies.  (Downing.) 12mo,  1 50 

BRIDGES,  ROOFS,  Etc. 

Cantilever— Highway— Suspension. 

Boiler’s  Highway  Bridges 8vo,  2 00 

* “ The  Thames  River  Bridge 4to,  paper,  5 00 

Burr’s  Stresses  in  Bridges 8vo,  3 50 

Merriman  & Jacoby’s  Text-book  of  Roofs  and  Bridges.  Part 

1.,  Stresses 8vo,  2 50 

Merriman  & Jacoby’s  Text-book  of  Roofs  and  Bridges.  Part 

11.,  Graphic  Statics 8vo,  2 50 

Merriman  & Jacoby’s  Text-book  of  Roofs  and  Bridges.  Part 

111.,  Bridge  Design 8vo,  5 00 

Merriman  & Jacoby’s  Text- book  of  Roofs  and  Bridges.  Part 

IV.,  Continuous,  Draw,  Cantilever,  Suspension,  and 

Arched  Bridges {In  preparation). 

Crehore’s  Mechanics  of  the  Girder 8vo,  5 00 

Du  Bois’s  Strains  in  Framed  Structures 4to,  10  00 

Greene’s ’Roof  Trusses 8vo,  1 25 

“ Bridge  Trusses 8vo,  2 50 

“ Arches  in  Wood,  etc 8vo,  2 50 

Waddell’s  Iron  Highway  Bridges 8vo,  4 00 

Wood’s  Construction  of  Bridges  and  Roofs 8vo,  2 00 

Foster’s  Wooden  Trestle  Bridges 4to,  5 00 

*Morison’s  The  Memphis  Bridge Oblong  4to,  10  00 

Johnson’s  Modern  Framed  Structures 4to,  10  00 

CHEMISTRY. 

Qualitative — Quantitative — Organic — Inorganic,  Etc. 


Fresenius’s  Qualitative  Chemical  Analysis.  (Johnson.) 8vo,  4 00 

“ Quantitative  Chemical  Analysis.  (Allen.) 8vo,  6 00 

**  “ “ “ (Bolton.) 8vo,  1 50 


4 


'Crafts’s  Qualitative  Analysis.  (Schaeffer.) 12ino,  $1  50 

Perkins’s  Qualitative  Analysis 12nio,  1 00 

Thorpe’s  Quantitative  Chemical  Analysis 18mo,  1 50 

Classen’s  Analysis  by  Electrolysis.  (Herrick.) *.  ..8vo,  3 00 

Stockbridge’s  Rocks  and  Soils 8vo,  2 50 

O’Brine’s  Laboratory  Guide  to  Chemical  Analysis 8vo,  2 00 

Mixter’s  Elementary  Text-book  of  Chemistry 12mo,  1 50 

Wulling’s  Inorganic  Phar.  and  Med.  Chemistry 12mo,  2 00 

Mandel’s  Bio-chemical  Laboratory 12mo,  1 50 

Austen’s  Notes  for  Chemical  Students 12mo,  1 50 

Schimpf’s  Volumetric  Analysis 12mo,  2 50 

Hammarsten’s  Physiological  Chemistry  (Maudel.) 8vo,  4 00 

Miller’s  Chemical  Physics 8vo,  2 00 

Pinner’s  Organic  Chemistry.  (Austen.) 12mo,  1 50 

N^olbe’s  Inorganic  Chemistry 12mo,  1 50 

Ricketts  and  Russell’s  Notes  on  Inorganic  Chemistry  (Non- 

metallic) Oblong  8vo,  morocco,  75 

Drechsel’s  Chemical  Reactions.  (Merrill.) 12mo,  1 25 

Adriance’s  Laboratory  Calculations 12mo,  1 25 

Troilius’s  Chemistry  of  Iron 8vo,  2 00 

Allen’s  Tables  for  Iron  Analysis 8vo,  3 00 

Nichols’s  Water  Supply  (Chemical  and  Sanitary) 8vo,  2 50 

Mason’s  “ “ 8vo,  5 00 

Spencer’s  Sugar  Manufacturer’s  Handbook . 12mo,  morocco  flaps,  2 00 

Wiechmann’s  Sugar  Analysis 8vo,  2 50 

“ Chemical  Lecture  Notes 12mo,  3 00 

DRAWING. 

Elementary — Geometrical — Topographical. 

Hill’s  Shades  and  Shadows  and  Perspective 8vo,  2 00 

Mahan’s  Industrial  Drawing.  (Thompson.) 2 vols.,  8vo,  3 50 

MacCord’s  Kinematics 8vo,  5 00 

“ Mechanical  Drawing 8vo,  4 00 

“ Descriptive  Geometry 8vo,  3 00 

Reed’s  Topographical  Drawing.  (II.  A.) 4to,  5 00 

Smith’s  Topographical  Drawing,  (Macmillan.) ...8vo,  2 50 

Warren’s  Free-hand  Drawing  .12mo,  1 00 


5 


Warren’s  Drafting  Instruments 12mo,  $1  25 

“ Projection  Drawing 12mo,  1 50 

“ Linear  Perspective 12mo,  1 00 

Plane  Problems 12mo,  1 25 

Primary  Geometry 12mo,  75 

“ Descriptive  Geometry 2 vols.,  8vo,  3 50 

“ Problems  and  Theorems 8vo,  2 50 

Machine  Construction 2 vols.,  8vo,  7 50 

“ Stereotomy — Stone  Cutting 8vo,  2 50 

“ Higher  Linear  Perspective  8vo,  3 50 

“ Shades  and  Shadows 8vo,  3 00 

Whelpley’s  Letter  Engraving 12mo,  2 00 


ELECTRICITY  AND  MAGNETISM. 

Illumination— Batteries— Physics. 

* Dredge’s  Electric  Illuminations. . . .2  vols.,  4to,  half  morocco,  25  00 


“ “ “ Vol.  II 4to,  7 50 

Kiaudet’s  Electric  Batteries.  (Fishback.) 12mo,  2 50 

Anthony  and  Brackett’s  Text-book  of  Physics 8vo,  4 00 

Cosmic  Law  of  Thermal  Repulsion 18mo,  75 

Thurston’s  Stationary  Steam  Engines  for  Electric  Lighting  Pur- 
poses  12mo,  1 50 

Michie’s  Wave  Motion  Relating  to  Sound  and  Light, 8vo,  4 00 

Barker’s  Deep-sea  Soundings 8vo,  2 00 

Holman’s  Precision  of  Measurements 8vo,  2 00 

Tillman’s  Heat 8vo,  1 50 

Gilbert’s  De-magnete.  (Mottelay.) 8vo,  2 50 

Benjamin’s  Voltaic  Cell 8vo,  3 00 

Reagan’s  Steam  and  Electrical  Locomotives 12mo  2 00 

ENGINEERING. 


Civil — Mechanical — Sanitary,  Etc. 


* Trautwine’s  Cross-section Sheet,  25 

* Civil  Engineer’s  Pocket-book.  ..12mo,  mor.  flaps,  5 00 

* “ ^ Excavations  and  Embankments 8vo,  2 00 

* “ Laying  Out  Curves 12mo,  morocco,  2 50 

Hudson’s  Excavation  Tables.  Vol.  II 8vo,  1 0(X 

6 


Searles’s  Fieia  Eugineering 13mo,  morocco  flaps, 

“ Railroad  Spiral 12mo,  morocco  flaps, 

Godwin’s  Railroad  Engineer’s  Field-book.  12mo,  pocket-bk.  form, 

Butts’s  Engineer’s  Field-book 12mo,  morocco. 

Gore’s  Elements  of  Goodesy 8vo, 

Wellington’s  Location  of  Railways 8vo, 

* Dredge’s  Penn.  Railroad  Construction,  etc.  . . Folio,  half  mor.. 

Smith’s  Cable  Tramways 4to, 

“ Wire  Manufacture  and  Uses 4to^ 

Mahan’s  Civil  Engineering.  (Wood.) 8vo, 

Wheeler’s  Civil  Engineering 8vo, 

Mosely’s  Mechanical  Engineering.  (Mahan.) 8vo, 

Johnson’s  Theory  and  Practice  of  Surveying 8vo, 

‘‘  Stadia  Reduction  Diagram.  .Sheet,  X 28^  inches, 

* Drinker’s  Tunnelling 4to,  half  morocco, 

Eissler’s  Explosives — Nitroglycerine  and  Dynamite 8vo, 

Foster’s  Wooden  Trestle  Bridges 4to, 

Ruffner’s  Non-tidal  Rivers 8vo, 

Greene’s  Roof  Trusses * 8vo, 

“ Bridge  Trusses 8vo, 

“ Arches  in  Wood,  etc 8vo, 

Church’s  Mechanics  of  Engineering — Solids  and  Fluids.  ...8vo, 

“ Notes  and  Examples  in  Mechanics 8vo, 

Howe’s  Retaining  Walls  (New  Edition.) 12mo, 

Wegmann’s  Construction  of  Masonry  Dams 4to, 

Thurston’s  Materials  of  Construction. 8vo, 

Baker’s  Masonry  Construction 8vo, 

“ Surveying  Instruments 12mo, 

Warren’s  Stereotomy — Stone  Cutting 8vo, 

Nichols’s  Water  Supply  (Chemical  and  Sanitary) 8vo, 

Mason’s  “ “ “ “ “ 8vo, 

Gerhard’s  Sanitary  House  Inspection 16mo, 

Kirkwood’s  Lead  Pipe  for  Service  Pipe 8vo, 

Wolff’s  Windmill  as  a Prime  Mover 8vo, 

Howard’s  Transition  Curve  Field-book 12mo,  morocco  flap, 

Crandall’s  The  Transition  Curve 12mo,  faiorocco. 


$3  00 

1 50 

2 50 
2 50 
2 50 
5 00 

20  00 

2 50 

3 00 
5 00 

4 00 

5 00 
4 00 

50 
25  00 

4 00 

5 00 
1 25 

1 25 

2 50 

2 50 

6 00 
2 00 

1 25 
5 00 
5 00 
5 00 

3 00 

2 50 

2 50 
5 00 
1 00 
1 50 

3 00 
1 50 
1 50 


7 


Crandall’s  Earthwork  Tables  8vo,  $1  50 

Patton’s  Civil  Engineering 8vo,  7 50 

“ Foundations 8vo,  5 00 

Carpenter’s  Experimental  Engineering  8vo,  6 00 

Webb’s  Engineering  Instruments 12mo,  morocco,  1 00 

Black’s  U.  S.  Public  Works 4to,  5 00 

Merriman  and  Brook’s  Handbook  for  Surveyors. . . .12mo,  mor.,  2 00 

Merriman’s  Retaining  Walls  and  Masonry  Dams 8vo,  2 00 

“ Geodetic  Surveying 8vo,  2 00 

Kiersted’s  Sewage  Disposal 12mo,  1 25 

Siebert  and  Biggin’s  Modern  Stone  Cutting  and  Masonry, . .8vo,  1 50 

Kent’s  Mechanical  Engineer’s  Pocket-book 12mo,  morocco,  5 00 


HYDRAULICS. 

Water-wheels — Windmills — Service  Pipe — Drainage,  Etc. 


Weisbach’s  Hydraulics.  (Du  Bois.) 8vo,  5 00 

Merrimau’s  Treatise  on  Hydraulics 8vo,  4 00 

Oanguillet&Kutter’s  Flow  of  Water.  (Hering& Trautwine.).8vo,  4 00 

Nichols’s  Water  Supply  (Chemical  and  Sanitary) 8vo,  2 50 

Wolff’s  Windmill  as  a Prime  Mover 8vo,  3 00 

Ferrel’s  Treatise  on  the  Winds,  Cyclones,  and  Tornadoes. . .8vo,  4 00 

Kirkwood’s  Lead  Pipe  for  Service  Pipe 8vo,  1 50 

Ruffner’s  Improvement  for  Non-tidal  Rivers 8vo,  1 25 

Wilson’s  Irrigation  Engineering 8vo,  4 00 

Bovey’s  Treatise  on  Hydraulics 8vo,  4 00 

Wegmann’s  Water  Supply  of  the  City  of  New  Y'ork 4to,  10  00 

Hazen’s  Filtration  of  Public  Water  Supply 8vo,  2 00 

Mason’s  Water  Supply — Chemical  and  Sanitary 8vo,  5 00 

Wood’s  Theory  of  Turbines 8vo,  2 50 

MANUFACTURES. 


Aniline — Boilers— Explosives— Iron— Sugar — Watches— 
Woollens,  Etc. 


Metcalfe’s  Cost  of  Manufactures 8vo,  5 00 

Metcalf’s  Steel  (Manual  for  Steel  Users) 12mo,  2 00 

Allen’s  Tables  for  Iron  Analysis 8vo,  3 00 


8 


West’s  American  Foundry  Practice .12mo,  $3  50 

“ Moulder’s  Text-book  12mo,  2 50 

Spencer’s  Sugar  Manufacturer’s  Handbook. . . .12mo,  mor.  flap,  2 00 

Wiechmauu’s  Sugar  Analysis 8vo,  2 50 

Beaumont’s  Woollen  and  Worsted  Manufacture 12mo,  1 50 

*Reisig’s  Guide  to  Piece  Dyeing 8vo,  25  00 

Eissler’s  Explosives,  Nitroglycerine  and  Dynamite 8vo,  4 00 

Keimann’s  Aniline  Colors.  (Crookes.). ...  8vo,  2 50 

Ford’s  Boiler  Making  for  Boiler  Makers 18mo,  1 00 

Thurston’s  Manual  of  Steam  Boilers 8vo,  5 00 

Booth’s  Clock  and  Watch  Maker’s  Manual 12mo,  2 00 

Holly’s  Saw  Filing 18mo,  75 

Svedelius’s  Handbook  for  Charcoal  Burners 12mo,  1 50 

The  Lathe  and  Its  Uses ,8vo,  6 00 

Woodbury’s  Fire  Protection  of  Mills 8vo,  2 50 

Holland’s  The  Iron  Founder 12mo,  2 50 

“ “ “ “ Supplement 12mo,  2 50 

“ Encyclopaedia  of  Founding  Terms 12mo,  3 00 

Bouvier’s  Handbook  on  Oil  Painting 12mo,  2 00 

Steven’s  House  Painting 18mo,  75 


MATERIALS  OF  ENGINEERING. 

Strength — Elasticity — Resistance,  Etc. 


Thurston’s  Materials  of  Engineering 3 vols.,  8vo,  8 00 

Vol.  L,  Non-metallic 8vo,  2 00 

Vol.  II.,  Iron  and  Steel 8vo,  3 50 

Vol.  HI.,  Alloys,  Brasses,  and  Bronzes 8vo,  2 50 

Thurston's  Materials  of  Construction 8vo,  5 00 

Baker’s  Masonry  Construction 8vo,  5 00 

Lanza’s  Applied  Mechanics 8vo,  7 50 

“ Strength  of  Wooden  Columns 8vo,  paper,  50 

Wood’s  Resistance  of  Materials 8vo,  2 00 

Weyrauch’s  Strength  of  Iron  and  Steel.  (Du  Bois.) 8vo,  1 50 

Burr’s  Elasticity  and  Resistance  of  Materials 8vo,  5 00 

Merriman’s  Mechanics  of  Materials 8vo,  4 00 

-Church’s  Mechanic’s  of  Engineering — Solids  and  Fluids 8vo,  6 00 

9 


Beardslee  and  Kent’s  Strength  of  Wrought  Iron 8vo,  $1  5' 

Hatfield’s  Transverse  Strains 8vo,  5 00'* 

Du  Bois’s  Strains  in  Framed  Structures 4to,  10  00 

Merrill’s  Stones  for  Building  and  Decoration 8vo,  5 00 

Bovey’s  Strength  of  Materials 8vo,  7 50 

Spalding’s  Roads  and  Pavements 12mo,  2 00 

Rockwell’s  Roads  and  Pavements  in  France 12mo,  1 25 

Byrne’s  Highway  Construction 8vo,  5 00 

Patton’s  Treatise  on  Foundations ,8vo,  5 OO^ 

MATHEMATICS. 

Calculus — Geometry — Trigonometry,  Etc. 

Rice  and  Johnson’s  Differential  Calculus 8vo,  3 50 

“ Abridgment  of  Differential  Calculus 8vo,  1 50' 

“ Differential  and  Integral  Calculus, 

2 vols.  in  1,  12mo,  2 50 

Johnson’s  Integral  Calculus 12mo,  1 50 

“ Curve  Tracing 12mo,  1 00 

“ Differential  Eq.uations — Ordinary  and  Partial 8vo,  3 50  ‘ 

“ Least  Squares 12mo,  1 50 

Craig’s  Linear  Differential  Equations 8vo,  5 00' 

Merriman  and  Woodward’s  Higher  Mathematics 8vo,  5 00' 

Bass’s  Differential  Calculus 12mo, 

Halsted’s  Synthetic  Geometry 8vo,  1 50» 

“ Elements  of  Geometry <,..8vo,  1 75- 

Chapman’s  Theory  of  Equations 12mo,  1 50' 

Merriman’s  Method  of  Least  S piares 8vo,  2 OO' 

Compton’s  Logarithmic  Computations 12mo,  1 50' 

Davis’s  Introduction  to  the  Logic  of  Algebra 8vo,  1 50- 

Warren’s  Primary  Geometry 12mo,  75- 

“ Plane  Problems.  , .12mo,  1 25- 

“ Descriptive  Geometry 2 vols.,  8vo,  3 50- 

“ Problems  and  Theorems .8vo,  2 50 

“ Higher  Linear  Perspective 8vo,  3 50- 

“ Free-hand  Drawing 12mo,  1 OO 

“ Drafting  Instruments 12mo,  1 25 


10 


Warren’s  Projection  Drawing. 12mo,  $1  50 

“ Linear  Perspective 12ino,  1 00 

“ Plane  Problems 12ino,  1 25' 

Searles’s  Elements  of  Geometry.  8vo,  1 50 

Brigg’s  Plane  Analytical  Geometry 12mo,  1 00 

Wood’s  Co-ordinate  Geometry 8vo,  2 00 

“ Trigonometry 12mo,  1 00 

Mahan’s  Descriptive  Geometry  (Stone  Cutting). ...  8vo,  1 50 

Woolf’s  Descriptive  Geometry Royal  8vo,  3 00 

Ludlow’s  Trigonometry  with  Tables.  (Bass.) 8vo,  3 00 

“ Logarithmic  and  Other  Tables.  (Bass.) 8vo,  2 00 

Baker’s  Elliptic  Functions. 8vo,  1 50 

Parker's  Quadrature  of  the  Circle 8vo,  2 50 

Totten’s  Metrology 8vo,  2 50 

Ballard’s  Pyramid  Problem 8vo,  1 50 

Barnard’s  Pyramid  Problem 8vo,  1 50 


MECHANICS-MACHINERY. 

Text-books  and  Practical  Works. 


Dana’s  Elementary  Mechanics 12mo,  1 50 

Wood’s  “ “ 12mo,  1 25 

“ ^ “ Supplement  and  Key ' 1 25 

“ Analytical  Mechanics 8vo,  3 00 

Michie’s  Analytical  Mechanics 8vo,  4 00 

Merriman’s  Mechanics  of  Materials 8vo,  4 00 

Church’s  Mechanics  of  Engineering. .....  8vo,  6 00 

“ Notes  and  Examples  in  Mechanics 8vo,  2 00 

Mosely’s  Mechanical  Engineering.  (Mahan.) 8vo,  5 00 

Weisbach’s  Mechanics  of  Engineering.  Vol.  III.,  Part  I., 

Sec.  I.  (Klein.) 8vo,  5 00 

Weisbach’s  Mechanics  of  Engineering.  Vol.  III.,  Part  I. 

Sec.  II.  (Klein.).. 8vo,  5 00 

Weisbacli’s  Hydraulics  and  Hydraulic  Motors.  (Du  Bois.)..8vo,  5 00 

“ Steam  Engines.  (Du  Bois.) 8vo,  5 00 

Lanza’s  Applied  Mechanics '. . . .8vo,  7 50> 


11 


Orehore’s  Mechanics  of  the  Girder 8vo,  $5  00 

MacCord’s  Kinematics 8vo,  5 00 

Thurston’s  Friction  and  Lost  Work 8vo,  3 00 

“ The  Animal  as  a Machine 12mo,  100 

Hall’s  Car  Lubrication. 12mo,  1 00 

Warren’s  Machine  Construction 2 vols.,  8vo,  7 50 

Chordal’s  Letters  to  Mechanics 12mo,  2 00 

The  Lathe  and  Its  Uses 8vo,  6 00 

Cromwell’s  Toothed  Gearing 12mo,  1 50 

“ Belts  and  Pulleys 12mo,  1 50 

Du  Bois’s  Mechanics.  Vol.  I.,  Kinematics 8vo,  3 50 

“ “ Vol.  II.,  Statics 8vo,  4 00 

“ “ Vol.  III.,  Kinetics 8vo,  3 50 

Dredge’s  .Trans.  Exhibits  Building,  World  Exposition, 

4to,  half  morocco,  15  00 

Flather’s  Dynamometers 12mo,  2 00 

“ Rope  Driving 12mo,  2 00 

Richards’s  Compressed  Air 12mo,  1 50 

, Smith’s  Press-working  of  Metals 8vo,  3 00 

Holly’s  Saw  Filing 18mo,  75 

Fitzgerald’s  Boston  Machinist 18mo,  1 00 

Baldwin’s  Steam  Heating  for  Buildings 12mo,  2 50 

Metcalfe’s  Cost  of  Manufactures 8vo,  5 00 

Benjamin’s  Wrinkles  and  Recipes 12mo,  2 00 

Dingey’s  Machinery  Pattern  Making. 12mo,  2 00 


METALLURGY. 

Iron— Gold— Silver — Alloys,  Etc. 


Egleston’s  Metallurgy  of  Silver 8vo,  7 50 

“ Gold  and  Mercury 8vo,  7 50 

“ Weights  and  Measures,  Tables 18mo,  75 

“ Catalogue  of  Minerals 8vo,  2 50 

O’Driscoll’s  Treatment  of  Gold  Ores 8vo,  2 00 

* Kerbs  Metallurgy — Copper  and  Iron 8vo,  15  00 

* “ “ Steel,  Fuel,  etc 8vo,  15  00 

12 


Thurston’s  Iron  and  Steel 8vo,  $3  50 

“ Alloys 8vo,  2 50 

Troilius’s  Chemistry  of  Iron 8vo,  2 00 

Kunhardt’s  Ore  Dressing  in  Europe 8vo,  1 50 

Weyrauch’s  Strength  of  Iron  and  Steel.  (Du  Bois.) 8vo,  1 50 

Beardslee  and  Kent’s  Strength  of  Wrought  Iron 8vo,  1 50 

Compton’s  First  Lessons  in  Metal  Working 12mo,  1 50 

West’s  American  Foundry  Practice 12mo,  2 50 

Moulder’s  Text-book 12mo,  2 50 

MINERALOGY  AND  MINING. 

Mine  Accidents— Ventilation— Ore  Dressing,  Etc. 

Dana’s  Descriptive  Mineralogy.  (E.  S.) 8vo,  half  morocco,  12  50 

“ Mineralogy  and  Petrography.  (J.  D.) 12mo,  2 00 

“ Text-book  of  Mineralogy.  (E.  S.) 8vo,  3 50 

“ Minerals  and  How  to  Study  Them.  (E.  S.) 12mo,  1 50 

• American  Eocalities  of  Minerals 8vo,  100 

Brush  and  Dana’s  Determinative  Mineralogy 8yo,  3 50 

Rosenbusch’s  Microscopical  Physiography  of  Minerals  and 

Rocks.  (Iddings.) 8vo,  5 00 

Hussak’s  Rock-forming  Minerals.*  (Smith.) 8vo,  2 00 

Williams’s  Lithology 8vo,  3 00 

Chester’s  Catalogue  of  Minerals 8vo,  1 25 

“ Dictionary  of  the  Names  of  Minerals 8vo,  3 00 

Egleston’s  Catalogue  of  Minerals  and  Synonyms 8vo,  2 50 

Goodyear’s  Coal  Mines  of  the  Western  Coast 12mo,  2 50 

Kunhardt’s  Ore  Dressing  in  Europe 8vo,  1 50 

Sawyer’s  Accidents  in  Mines 8vo,  7 00 

Wilson’s  Mine  Ventilation 16mo,  1 25 

Boyd’s  Resources  of  South  Western  Virginia 8vo,  3 00 

“ Map  of  South  Western  Virginia Pocket-book  form,  2 00 

Stockbridge’s  Rocks  and  Soils 8vo,  2 50 

Eissler’s  Explosives — Nitroglycerine  and  Dynamite 8vo,  4 00 

13 


^Drinker’s  Tunnelling,  Explosives,  Compounds,  and  Roek  Drills. 

“4to,  half  morocco,  $25  00 

Beard’s  Ventilation  of  Mines 12mo,  2 50 

Ihlseng’s  Manual  of  Mining. 8vo,  4 00 

STEAM  AND  ELECTRICAL  ENGINES,  BOILERS,  Etc. 

Stationaky— Marine— Locomotive— Gas  Engines,  Etc. 


Weisbach’s  Steam  Engine.  (Du  Bois.) 8vo,  5 00 

Thurston’s  Engine  and  Boiler  Trials 8vo,  5 00 

“ Philosophy  of  the  Steam  Engine 12mo,  75 

“ Stationary  Steam  Engines 12mo,  150 

Boiler  Explosion 12mo,  1 50 

“ Steam-boiler  Construction  and  Operation 8vo, 


Reflection  on  the  Motive  Power  of  Heat.  (Carnot.) 

12mo,  2 00 

Thurston’s  Manual  of  the  Steam  Engine.  Part  I.,  Structure 


and  Theory 8vo,  7 50 

Thurston’s  Manual  of  the  Steam  Engine.  Part  II.,  Design, 

Construction,  and  Operation 8vo,  7 50 

2 parts,  12  00 

Rontgen’s  Thermodynamics.  (Du  Bois.) 8vo,  5 00 

Peabody’s  Thermodynamics  of  the  Steam  Engine 8vo,  5 00 

“ Valve  Gears  for  the  Steam-Engine 8vo,  2 50 

" Tables  of  Saturated  Steam 8vo,  1 00 

Wood’s  Thermodynamics,  Heat  Motors,  etc 8vo,  4 00 

Pupin  and  Osterberg’s  Thermodynamics 12mo,  1 25 

Kneass’s  Practice  and  Theory  of  the  Injector 8vo,  1 50 

Reagan’s  Steam  and  Electrical  Locomotives 12mo,  2 00 

Meyer’s  Modern  Locomotive  Construction 4to,  10  00 

Whitham’s  Steam-engine  Design 8vo,  6 00 

“ Constructive  Steam  Engineering 8vo,  10  00 

Hemenway’s  Indicator  Practice 12mo,  2 00 

Pray’s  Twenty  Years  with  the  Indicator Royal  8vo,  2 50 

Spangler’s  Valve  Gears 8vo,  2 50 

* Maw’s  Marine  Engines Folio,  half  morocco,  18  00 

Trowbridge’s  Stationary  Steam  Engines 4to,  boards,  2 50 

14 


I’ord’s  Boiler  Making  for  Boiler  Makers 18mo,  $1  00 

'Wilson’s  Steam  Boilers.  (Flather.) 12mo,  2 50 

Baldwin’s  Steam  Heating  for  Buildings 12mo,  2 50 

Hoadley’s  Warm-blast  Furnace 8vo,  1 50 

Sinclair’s  Locomotive  Ruqning 12mo,  2 00 

'(Clerk’s  Gas  Engine 12mo,  4 00 

TABLES,  WEIGHTS,  AND  MEASURES. 

For  Engineers,  Mechanics,  Actuaries— Metric  Tables,  Etc. 

(Crandall’s  Railway  and  Earthwork  Tables 8vo,  1 50 

Johnson’s  Stadia  and  Earthwork  Tables 8vo,  1 25 

Bixby’s  Graphical  Computing  Tables Sheet,  25 

Compton’s  Logarithms 12mo,  1 50 

Ludlow’s  Logarithmic  and  Other  Tables.  (Bass.) 12mo,  2 00 

Thurston’s  Conversion  Tables 8vo,  1 00 

Hgleston’s  Weights  and  Measures 18mo,  75 

Totten’s  Metrology 8vo,  2 50 

Eisher’s  Table  of  Cubic  Yards Cardboard,  25 

iHudson’s  Excavation  Tables.  Vol.  II 8vo,  100 

VENTILATION. 

Steam  Heating — House  Inspection — Mine  Ventilation. 

Beard’s  Ventilation  of  Mines 12mo,  2 50 

Baldwin’s  Steam  Heating 12mo,  2 50 

Reid’s  Ventilation  of  American  Dwellings 12mo,  1 50 

Mott’s  The  Air  We  Breathe,  and  Ventilation 16mo,  1 00 

Gerhard’s  Sanitary  House  Inspection Square  16mo,  1 00 

Wilson’s  Mine  Ventilation 16mo,  1 25 

•Carpenter’s  Heating  and  Ventilating  of  Buildings 8vo,  3 00 

niSCELLANEOUS  PUBLICATIONSo 

Alcott’s  Gems,  Sentiment,  Language Gilt  edges,  5 00 

Bailey’s  The  New  Tale  of  a Tub 8vo,  75 

Ballard’s  Solution  of  the  Pyramid  Problem 8vo,  1 50 

-Barnard’s  The  Metrological  System  of  the  Great  Pyrarnid.  .8vo,  1 50 

15 


*■  Wiley’s  Yosemite,  Alaska,  and  Yellowstone 4to,  |3  00*- 

Emmon’s  Geological  Guide-book  of  the  Rocky  Mountains.  .8vo,  1 50- 

Ferrel’s  Treatise  on  the  Winds 8vo,  4 00 

Perkins’s  Cornell  University Oblong  4to,  1 50 

Ricketts’s  History  of  Rensselaer  Polytechnic  Institute 8vo,  3 00 

Mott’s  The  Fallacy  of  the  Present  Theory  of  Sound.  .Sq.  lOnio,  1 00 

Rotherham’s  The  New  Testament  Critically  Emphathized. 


12mo,  1 50 

Totten’s  An  Important  Question  in  Metrology 8vo,  2 50 

Whitehouse*s  Lake  Moeris Paper,  25- 


HEBREW  AND  CHALDEE  TEXT=BOOKS. 

For  Schools  and  Theological  Seminaries. 

Gesenius’s  Hebrew  and  Chaldee  Lexicon  to  Old  Testament. 

(Tregelles.) Small  4to,  half  morocco,  5 00 

Green’s  Grammar  of  the  Hebrew  Language  (New  Edition). 8vo,  3 00 

“ Elementary  Hebrew  Grammar. 12mo,  1 25 

“ Hebrew  Chrestomathy 8vo,  2 00 

Letteris’s  Hebrew  Bible  (Massoretic  Notes  in  English). 

8vo,  arabesque,  2 25 

Luzzato’s  Grammar  of  the  Biblical  Chaldaic  Language  and  the 

Talmud  Babli  Idioms 12mo,  1 50 

MEDICAL. 

Bull’s  Maternal  Management  in  Health  and  Disease 12mo,  1 00 

Mott’s  Composition,  Digestibility,  and  Nutritive  Value  of  Food. 

Large  mounted  chart,  1 25 

Steel’s  Treatise  on  the  Diseases  of  the  Ox 8vo,  6 00 

“ Treatise  on  the  Diseases  of  the  Dog 8vo,  3 50 

Worcester’s  Small  Hospitals — Establishment  and  Maintenance, 
including  Atkinson’s  Suggestions  for  Hospital  Archi- 
tecture  12mo,  1 25 

HaminaiiS ten's  Physiological  Chemistry.  (Mandel.) 8vo,  4 00 


16 


. -1/^i 

(^Ud^4M^c^  (l^%c4^'<^- 
^U  '^vPfjJXA^  ccvfc^  a 
(Pl  Oi^-t  /iXTrcC  ^ l i ^-' 

^ h((/yi  (Ly(rZ(ytM<j 

kJl  i^  4\^4{  ^Cdj-uaji  t yl  'ich 


hi- \4‘C  v^i-i'V^c-  i i )r^'7PL  C_  ■ t- 

^ / 


hivl<^iuL- 

V.' 


ivtCf  ^IalJ' 


()a  (U/TiA^<-'J 

H /c  j A^irf 


6/^ 

'dUt\.  ')izly(. 


-! 


Lt 


V 

Si 


-r 


i 


7 


•V. 


Qifl 


3 0112  105365297 


p#p9H 

URg^m 

fW^ 

